Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Summary Collateral Information
	Description
Group 1
Pool 8043	Option ARM
Pool 8044	Option ARM

General Information
Description	Total	Pool 8043	Pool 8044	Group 1
Weighted Average Pass Through Rate	6.43868%	7.38694%	6.42678%	6.43868%
Weighted Average Mortgage Interest Rate	7.68267%	7.76194%	7.68167%	7.68267%
Weighted Average Remaining Term (in Months)	400.50281	361.28045	400.91849	400.50281
Weighted Average Loan Age (in Months)	9.36472	10.87858	9.34868	9.36472
Average Ending Scheduled Principal Balance	$550,080.28	$688,538.81	$548,910.44	$550,080.28
Remaining Loan Count	1671	14	1657	1671
Ending Scheduled Principal Balance	$919,184,144.82	$9,639,543.29	$909,544,601.53	$919,184,144.82

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Geographic Distribution
Total			Pool 8043			Pool 8044
State	Percent	Ending Scheduled Principal Balance	State	Percent	Ending Scheduled Principal Balance	State	Percent	Ending Scheduled Principal Balance
CA	$587,835,182.95	63.95%	CA	$6,176,270.86	64.07%	CA	$581,658,912.09	63.95%
FL	$97,141,186.41	10.57%	IL	$3,106,985.33	32.23%	FL	$97,141,186.41	10.68%
AZ	$33,411,306.59	3.63%	AZ	$193,664.34	2.01%	AZ	$33,217,642.25	3.65%
NY	$27,608,269.73	3.00%	WA	$162,622.76	1.69%	NY	$27,608,269.73	3.04%
WA	$26,325,834.29	2.86%	-	$0.00	0.00%	WA	$26,163,211.53	2.88%
OTHER	$146,862,364.85	15.98%	OTHER	$0.00	-0.00%	OTHER	$143,755,379.52	15.81%

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Geographic Distribution
Group 1
State	Percent	Ending Scheduled Principal Balance
CA	$587,835,182.95	63.95%
FL	$97,141,186.41	10.57%
AZ	$33,411,306.59	3.63%
NY	$27,608,269.73	3.00%
WA	$26,325,834.29	2.86%
OTHER	$146,862,364.85	15.98%

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Prepayment Information (all groups)
	1 Month	3 Month	6 Month	12 Month	Cumulative
PSA	669.40969%	1059.56174%	1563.45600%	2222.14331%	2222.13785%
CPR	12.53767%	17.73341%	21.51516%	24.00496%	24.00494%
SMM	1.11014%	1.61355%	1.99863%	2.26155%	2.26155%

Trigger Events
	Trigger Flag
Optional Termination Date Has Occurred; 1=Yes, 0=No	0
Senior Prepayment Step-Down Has Occurred; 1=Yes, 0=No	0
Senior Credit Support Depletion Date Has Occurred; 1=Yes, 0=No	0

Comments

1. The Class B Certificates provide, to the limited extent described in the Prospectus Supplement, credit support, to certain Senior Certificates. The "Prospectus Supplement" is that certain Prospectus Supplement, dated January 23, 2007 to that certain Prospectus Supplement, dated January 11, 2007, to which certain Senior Certificates were offered.

2. The MBA method of delinquency calculation is used.

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Certificate Payment Summary Report
Class	CUSIP	Original Principal/Notional Balance	Beginning Principal/Notional Balance	Interest Distribution	Principal Distribution	Principal Loss	Deferred Interest	Total Distribution	Ending Principal/Notional Balance
A1A	92926WAA5	$807,437,000.00	$668,598,500.29	$3,166,554.64	$5,745,801.81	$0.00	$0.00	$8,912,356.45	$662,852,698.48
A1B	92926WAB3	$100,930,000.00	$83,575,123.06	$371,299.87	$718,227.90	$0.00	$0.00	$1,089,527.77	$82,856,895.16
A1C	92926WAC1	$100,930,000.00	$83,575,123.06	$374,085.70	$718,227.90	$0.00	$0.00	$1,092,313.60	$82,856,895.16
X1PPP	92926WAD9	$0.00	$0.00	$660,814.73	$0.00	$0.00	$0.00	$660,814.73	$0.00
X1PPP_NOTIONAL	XXXXXXXXX	$1,100,051,573.00	$926,366,937.80	$660,814.79	$0.00	$0.00	$0.00	$660,814.79	$919,184,144.82
X1PPP_PRINCIPAL	XXXXXXXXX	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
X2	92926WAE7	$103,110,256.00	$11,480,742.22	$12,475.16	$0.00	$0.00	$0.00	$12,475.16	$9,639,543.29
B1	92926WAF4	$17,051,000.00	$17,025,395.18	$77,908.91	$100.59	$0.00	$0.00	$78,009.50	$17,025,294.59
B2	92926WAG2	$17,600,000.00	$17,573,570.77	$80,563.83	$103.83	$0.00	$0.00	$80,667.66	$17,573,466.94
B3	92926WAH0	$5,500,000.00	$5,491,740.87	$25,221.96	$32.45	$0.00	$0.00	$25,254.41	$5,491,708.42
B4	92926WAJ6	$6,600,000.00	$6,590,089.03	$30,376.19	$38.93	$0.00	$0.00	$30,415.12	$6,590,050.10
B5	92926WAK3	$5,500,000.00	$5,491,740.87	$25,450.79	$32.45	$0.00	$0.00	$25,483.24	$5,491,708.42

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Certificate Payment Summary Report (Continued)
Class	CUSIP	Original Principal/Notional Balance	Beginning Principal/Notional Balance	Interest Distribution	Principal Distribution	Principal Loss	Deferred Interest	Total Distribution	Ending Principal/Notional Balance
B6	92926WAL1	$4,400,000.00	$4,393,392.68	$20,470.46	$25.96	$0.00	$0.00	$20,496.42	$4,393,366.72
B7	92926WAM9	$3,850,000.00	$3,844,218.61	$18,840.68	$22.71	$0.00	$0.00	$18,863.39	$3,844,195.90
B8	92926WAN7	$2,750,000.00	$2,745,870.42	$13,915.27	$16.22	$0.00	$0.00	$13,931.49	$2,745,854.20
B9	92926WAP2	$4,400,000.00	$4,393,392.68	$23,179.72	$25.96	$0.00	$0.00	$23,205.68	$4,393,366.72
B10	92926WAQ0	$6,050,000.00	$6,040,914.96	$31,872.12	$35.69	$0.00	$0.00	$31,907.81	$6,040,879.27
B11	92926WAR8	$4,400,000.00	$4,393,392.68	$23,179.72	$25.96	$0.00	$0.00	$23,205.68	$4,393,366.72
B12	92926WAT4	$2,750,000.00	$2,745,870.42	$14,487.33	$16.22	$0.00	$0.00	$14,503.55	$2,745,854.20
B13	92926WAU1	$2,750,000.00	$2,745,870.42	$14,487.33	$16.22	$0.00	$0.00	$14,503.55	$2,745,854.20
B14	92926WAV9	$7,153,473.81	$7,142,731.74	$37,685.35	$42.02	$0.12	$0.00	$37,727.37	$7,142,689.60
R	92926WAS6	$100.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
R_SYN	XXXXXXXXX	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
TFEE	XXXXXXXXX	$0.00	$0.00	$617.58	$0.00	$0.00	$0.00	$617.58	$0.00
Total*		$1,100,051,573.81	$926,366,937.74	$5,022,869.73	$7,182,792.82	$0.12	$0.00	$12,205,662.58	$919,184,144.80

*Total balances exclude notional balances.

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Total Funds Available for Distribution
PRINCIPAL BALANCE
Scheduled Principal Received or Advanced	($3,136,007.82)
Unscheduled Principal	$335,163.53
Prepayments in Full	$9,983,637.27
Repurchases	$0.00
Liquidations	$0.00
Total Principal	$7,182,792.98
INTEREST
Accrued Interest at Gross Rate	$5,930,806.07
Relief Act Shortfall	$0.00
Prepayment Interest Shortfall	$0.00
Servicing Fees	$960,326.03
Other	$0.00
Total Interest	$4,970,479.58
ADDITIONAL FUNDS
Excess Liquidation Proceeds	$0.00
Subsequent Recoveries	$0.00
Prepayment Penalties	$52,389.97

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Total Funds Available for Distribution
ADDITIONAL FUNDS
Other	$0.00
Total Additional Funds	$52,389.97
Total Funds Available for Distribution	$12,153,272.56

Certificate Payment Report - Principal
Class	CUSIP	Beginning Principal/Notional Balance	Principal Distribution	Principal Loss	Principal Reimbursed	Subsequent Recoveries	Deferred Interest	Total Principal Distribution	Ending Principal/Notional Balance
A1A	92926WAA5	$668,598,500.29	$5,745,801.81	$0.00	$0.00	$0.00	$0.00	$5,745,801.81	$662,852,698.48
A1B	92926WAB3	$83,575,123.06	$718,227.90	$0.00	$0.00	$0.00	$0.00	$718,227.90	$82,856,895.16
A1C	92926WAC1	$83,575,123.06	$718,227.90	$0.00	$0.00	$0.00	$0.00	$718,227.90	$82,856,895.16
X1PPP	92926WAD9	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
X1PPP_NOTIONAL	XXXXXXXXX	$926,366,937.80	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$919,184,144.82
X1PPP_PRINCIPAL	XXXXXXXXX	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
X2	92926WAE7	$11,480,742.22	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$9,639,543.29
B1	92926WAF4	$17,025,395.18	$100.59	$0.00	$0.00	$0.00	$0.00	$100.59	$17,025,294.59
B2	92926WAG2	$17,573,570.77	$103.83	$0.00	$0.00	$0.00	$0.00	$103.83	$17,573,466.94

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Certificate Payment Report - Principal (Continued)
Class	CUSIP	Beginning Principal/Notional Balance	Principal Distribution	Principal Loss	Principal Reimbursed	Subsequent Recoveries	Deferred Interest	Total Principal Distribution	Ending Principal/Notional Balance
B3	92926WAH0	$5,491,740.87	$32.45	$0.00	$0.00	$0.00	$0.00	$32.45	$5,491,708.42
B4	92926WAJ6	$6,590,089.03	$38.93	$0.00	$0.00	$0.00	$0.00	$38.93	$6,590,050.10
B5	92926WAK3	$5,491,740.87	$32.45	$0.00	$0.00	$0.00	$0.00	$32.45	$5,491,708.42
B6	92926WAL1	$4,393,392.68	$25.96	$0.00	$0.00	$0.00	$0.00	$25.96	$4,393,366.72
B7	92926WAM9	$3,844,218.61	$22.71	$0.00	$0.00	$0.00	$0.00	$22.71	$3,844,195.90
B8	92926WAN7	$2,745,870.42	$16.22	$0.00	$0.00	$0.00	$0.00	$16.22	$2,745,854.20
B9	92926WAP2	$4,393,392.68	$25.96	$0.00	$0.00	$0.00	$0.00	$25.96	$4,393,366.72
B10	92926WAQ0	$6,040,914.96	$35.69	$0.00	$0.00	$0.00	$0.00	$35.69	$6,040,879.27
B11	92926WAR8	$4,393,392.68	$25.96	$0.00	$0.00	$0.00	$0.00	$25.96	$4,393,366.72
B12	92926WAT4	$2,745,870.42	$16.22	$0.00	$0.00	$0.00	$0.00	$16.22	$2,745,854.20
B13	92926WAU1	$2,745,870.42	$16.22	$0.00	$0.00	$0.00	$0.00	$16.22	$2,745,854.20
B14	92926WAV9	$7,142,731.74	$42.02	$0.12	$0.00	$0.00	$0.00	$42.02	$7,142,689.60
R	92926WAS6	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Certificate Payment Report - Principal (Continued)
Class	CUSIP	Beginning Principal/Notional Balance	Principal Distribution	Principal Loss	Principal Reimbursed	Subsequent Recoveries	Deferred Interest	Total Principal Distribution	Ending Principal/Notional Balance
R_SYN	XXXXXXXXX	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
TFEE	XXXXXXXXX	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
Total *		$926,366,937.74	$7,182,792.82	$0.12	$0.00	$0.00	$0.00	$7,182,792.82	$919,184,144.80

*Total balances exclude notional balances.

Certificate Payment Report - Interest
Class	Beginning Principal/Notional Balance	Interest Rate Accrued	Interest Rate Paid	Interest Accrued	Prepayment Interest Shortfall	Relief Act Shortfall	Other Interest Shortfall	Unscheduled Interest	Interest Reimbursed	Carryforward Amount Paid	Total Interest Distributed	Total Carryforward Amount Remaining
A1A	$668,598,500.29	5.6833300000%	5.6833300000%	$3,166,554.93	$0.00	$0.00	$0.00	($0.29)	$0.00	$0.00	$3,166,554.64	$0.00
A1B	$83,575,123.06	5.3312500000%	5.3312500000%	$371,299.90	$0.00	$0.00	$0.00	($0.03)	$0.00	$0.00	$371,299.87	$0.00
A1C	$83,575,123.06	5.3712500000%	5.3712500000%	$374,085.73	$0.00	$0.00	$0.00	($0.03)	$0.00	$0.00	$374,085.70	$0.00
X1PPP	$0.00	0.0000000000%	0.0000000000%	$608,424.82	$0.00	$0.00	$0.00	($0.06)	$0.00	$0.00	$660,814.73	$0.00
X1PPP_NOTIONAL	$926,366,937.80	0.7881431746%	0.8560082572%	$608,424.82	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$660,814.79	$0.00

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Certificate Payment Report - Interest (Continued)
Class	Beginning Principal/Notional Balance	Interest Rate Accrued	Interest Rate Paid	Interest Accrued	Prepayment Interest Shortfall	Relief Act Shortfall	Other Interest Shortfall	Unscheduled Interest	Interest Reimbursed	Carryforward Amount Paid	Total Interest Distributed	Total Carryforward Amount Remaining
X1PPP_PRINCIPAL	$0.00	0.0000000000%	0.0000000000%	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
X2	$11,480,742.22	1.3039398478%	1.3039398478%	$12,475.16	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$12,475.16	$0.00
B1	$17,025,395.18	5.4912500000%	5.4912500000%	$77,908.92	$0.00	$0.00	$0.00	($0.01)	$0.00	$0.00	$77,908.91	$0.00
B2	$17,573,570.77	5.5012500000%	5.5012500000%	$80,563.84	$0.00	$0.00	$0.00	($0.01)	$0.00	$0.00	$80,563.83	$0.00
B3	$5,491,740.87	5.5112500000%	5.5112500000%	$25,221.96	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$25,221.96	$0.00
B4	$6,590,089.03	5.5312500000%	5.5312500000%	$30,376.19	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$30,376.19	$0.00
B5	$5,491,740.87	5.5612500000%	5.5612500000%	$25,450.79	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$25,450.79	$0.00
B6	$4,393,392.68	5.5912500000%	5.5912500000%	$20,470.46	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$20,470.46	$0.00
B7	$3,844,218.61	5.8812500000%	5.8812500000%	$18,840.68	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$18,840.68	$0.00
B8	$2,745,870.42	6.0812500000%	6.0812500000%	$13,915.27	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$13,915.27	$0.00
B9	$4,393,392.68	6.3312500000%	6.3312500000%	$23,179.72	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$23,179.72	$0.00
B10	$6,040,914.96	6.3312500000%	6.3312500000%	$31,872.12	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$31,872.12	$0.00
B11	$4,393,392.68	6.3312500000%	6.3312500000%	$23,179.72	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$23,179.72	$0.00

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Certificate Payment Report - Interest (Continued)
Class	Beginning Principal/Notional Balance	Interest Rate Accrued	Interest Rate Paid	Interest Accrued	Prepayment Interest Shortfall	Relief Act Shortfall	Other Interest Shortfall	Unscheduled Interest	Interest Reimbursed	Carryforward Amount Paid	Total Interest Distributed	Total Carryforward Amount Remaining
B12	$2,745,870.42	6.3312500000%	6.3312500000%	$14,487.33	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$14,487.33	$0.00
B13	$2,745,870.42	6.3312500000%	6.3312500000%	$14,487.33	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$14,487.33	$0.00
B14	$7,142,731.74	6.3312500000%	6.3312500000%	$37,685.35	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$37,685.35	$0.00
R	$0.00	0.0000000000%	0.0000000000%	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
R_SYN	$0.00	0.0000000000%	0.0000000000%	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
TFEE	$0.00	0.0000000000%	0.0000000000%	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$617.58	$0.00
Total *	$926,366,937.74			$4,970,480.22	$0.00	$0.00	$0.00	($0.46)	$0.00	$0.00	$5,022,869.73	$0.00

*Total balances exclude notional balances.

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Principal Factors Report
Class	Original Scheduled Balance	Beginning Principal/Notional Balance	Principal Loss	Principal Reimbursed	Subsequent Recoveries	Deferred Interest	Total Principal	Ending Principal/Notional Balance Percent	Ending Principal/Notional Balance
A1A	$807,437,000.00	828.05036218	0.00000000	0.00000000	0.00000000	0.00000000	7.11609923	0.8209342630	820.93426296
A1B	$100,930,000.00	828.05036223	0.00000000	0.00000000	0.00000000	0.00000000	7.11609928	0.8209342630	820.93426295
A1C	$100,930,000.00	828.05036223	0.00000000	0.00000000	0.00000000	0.00000000	7.11609928	0.8209342630	820.93426295
X1PPP	$0.00	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.0000000000	0.00000000
X1PPP_NOTIONAL	$1,100,051,573.00	842.11227958	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.8355827739	835.58277392
X1PPP_PRINCIPAL	$0.00	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.0000000000	0.00000000
X2	$103,110,256.00	111.34432854	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.0934877253	93.48772531
B1	$17,051,000.00	998.49833910	0.00000000	0.00000000	0.00000000	0.00000000	0.00589936	0.9984924397	998.49243974
B2	$17,600,000.00	998.49833920	0.00000000	0.00000000	0.00000000	0.00000000	0.00589943	0.9984924398	998.49243977
B3	$5,500,000.00	998.49834000	0.00000000	0.00000000	0.00000000	0.00000000	0.00590000	0.9984924400	998.49244000
B4	$6,600,000.00	998.49833788	0.00000000	0.00000000	0.00000000	0.00000000	0.00589848	0.9984924394	998.49243939

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Principal Factors Report (Continued)
Class	Original Scheduled Balance	Beginning Principal/Notional Balance	Principal Loss	Principal Reimbursed	Subsequent Recoveries	Deferred Interest	Total Principal	Ending Principal/Notional Balance Percent	Ending Principal/Notional Balance
B5	$5,500,000.00	998.49834000	0.00000000	0.00000000	0.00000000	0.00000000	0.00590000	0.9984924400	998.49244000
B6	$4,400,000.00	998.49833636	0.00000000	0.00000000	0.00000000	0.00000000	0.00590000	0.9984924364	998.49243636
B7	$3,850,000.00	998.49834026	0.00000000	0.00000000	0.00000000	0.00000000	0.00589870	0.9984924416	998.49244156
B8	$2,750,000.00	998.49833455	0.00000000	0.00000000	0.00000000	0.00000000	0.00589818	0.9984924364	998.49243636
B9	$4,400,000.00	998.49833636	0.00000000	0.00000000	0.00000000	0.00000000	0.00590000	0.9984924364	998.49243636
B10	$6,050,000.00	998.49834050	0.00000000	0.00000000	0.00000000	0.00000000	0.00589917	0.9984924413	998.49244132
B11	$4,400,000.00	998.49833636	0.00000000	0.00000000	0.00000000	0.00000000	0.00590000	0.9984924364	998.49243636
B12	$2,750,000.00	998.49833455	0.00000000	0.00000000	0.00000000	0.00000000	0.00589818	0.9984924364	998.49243636
B13	$2,750,000.00	998.49833455	0.00000000	0.00000000	0.00000000	0.00000000	0.00589818	0.9984924364	998.49243636
B14	$7,153,473.81	998.49834216	0.00001678	0.00000000	0.00000000	0.00000000	0.00587407	0.9984924513	998.49245132
R	$100.00	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.0000000000	0.00000000
R_SYN	$0.00	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.0000000000	0.00000000
TFEE	$0.00	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.0000000000	0.00000000

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Principal Factors Report (Continued)
Class	Original Scheduled Balance	Beginning Principal/Notional Balance	Principal Loss	Principal Reimbursed	Subsequent Recoveries	Deferred Interest	Total Principal	Ending Principal/Notional Balance Percent	Ending Principal/Notional Balance

Interest Factors Report
Class	Original Balance	Interest Rate Accrued	Interest Rate Paid	Current Month Interest Accrued	Prepayment Interest Shortfall	Relief Act Interest Shortfall	Other Interest Shortfall	Unscheduled Interest	Interest Reimbursed	Carryforward Amount Paid	Deferred Interest	Total Interest Distribution	Total Carryforward Amount Remaining
A1A	$807,437,000.00	5.6833300000%	5.6833300000%	3.92173622	0.00000000	0.00000000	0.00000000	-0.00000036	0.00000000	0.00000000	0.00000000	3.92173586	0.00000000
A1B	$100,930,000.00	5.3312500000%	5.3312500000%	3.67878629	0.00000000	0.00000000	0.00000000	-0.00000030	0.00000000	0.00000000	0.00000000	3.67878599	0.00000000
A1C	$100,930,000.00	5.3712500000%	5.3712500000%	3.70638789	0.00000000	0.00000000	0.00000000	-0.00000030	0.00000000	0.00000000	0.00000000	3.70638760	0.00000000
X1PPP	$0.00	0.0000000000%	0.0000000000%	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000
X1PPP_NOTIONAL	$1,100,051,573.00	0.7881431746%	0.8560082572%	0.55308754	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.60071255	0.00000000
X1PPP_PRINCIPAL	$0.00	0.0000000000%	0.0000000000%	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000
X2	$103,110,256.00	1.3039398478%	1.3039398478%	0.12098855	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.12098855	0.00000000
B1	$17,051,000.00	5.4912500000%	5.4912500000%	4.56917014	0.00000000	0.00000000	0.00000000	-0.00000059	0.00000000	0.00000000	0.00000000	4.56916955	0.00000000
B2	$17,600,000.00	5.5012500000%	5.5012500000%	4.57749091	0.00000000	0.00000000	0.00000000	-0.00000057	0.00000000	0.00000000	0.00000000	4.57749034	0.00000000

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Interest Factors Report (Continued)
Class	Original Balance	Interest Rate Accrued	Interest Rate Paid	Current Month Interest Accrued	Prepayment Interest Shortfall	Relief Act Interest Shortfall	Other Interest Shortfall	Unscheduled Interest	Interest Reimbursed	Carryforward Amount Paid	Deferred Interest	Total Interest Distribution	Total Carryforward Amount Remaining
B3	$5,500,000.00	5.5112500000%	5.5112500000%	4.58581091	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	4.58581091	0.00000000
B4	$6,600,000.00	5.5312500000%	5.5312500000%	4.60245303	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	4.60245303	0.00000000
B5	$5,500,000.00	5.5612500000%	5.5612500000%	4.62741636	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	4.62741636	0.00000000
B6	$4,400,000.00	5.5912500000%	5.5912500000%	4.65237727	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	4.65237727	0.00000000
B7	$3,850,000.00	5.8812500000%	5.8812500000%	4.89368312	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	4.89368312	0.00000000
B8	$2,750,000.00	6.0812500000%	6.0812500000%	5.06009818	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	5.06009818	0.00000000
B9	$4,400,000.00	6.3312500000%	6.3312500000%	5.26811818	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	5.26811818	0.00000000
B10	$6,050,000.00	6.3312500000%	6.3312500000%	5.26811901	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	5.26811901	0.00000000
B11	$4,400,000.00	6.3312500000%	6.3312500000%	5.26811818	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	5.26811818	0.00000000
B12	$2,750,000.00	6.3312500000%	6.3312500000%	5.26812000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	5.26812000	0.00000000
B13	$2,750,000.00	6.3312500000%	6.3312500000%	5.26812000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	5.26812000	0.00000000
B14	$7,153,473.81	6.3312500000%	6.3312500000%	5.26811882	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	5.26811882	0.00000000
R	$100.00	0.0000000000%	0.0000000000%	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Interest Factors Report (Continued)
Class	Original Balance	Interest Rate Accrued	Interest Rate Paid	Current Month Interest Accrued	Prepayment Interest Shortfall	Relief Act Interest Shortfall	Other Interest Shortfall	Unscheduled Interest	Interest Reimbursed	Carryforward Amount Paid	Deferred Interest	Total Interest Distribution	Total Carryforward Amount Remaining
R_SYN	$0.00	0.0000000000%	0.0000000000%	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000
TFEE	$0.00	0.0000000000%	0.0000000000%	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Collateral Report Pool 8043
LOAN COUNT
Original Loan Count	110
Beginning Loan Count	16
Loans Added	0
Loans Prepaid-in-full	2
Loans Liquidated-in-full	0
Loans Repurchased	0
Ending Loan Count	14
PRINCIPAL BALANCE
Original Scheduled Principal Balance	$103,110,256.45
Beginning Scheduled Principal Balance	$11,480,742.22
Scheduled Principal Received or Advanced	($34,582.56)
Unscheduled Principal	$5,219.95
Prepayments-in-full	$1,870,561.54

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Collateral Report Pool 8043 (Continued)
PRINCIPAL BALANCE
Liquidations-in-full	$0.00
Repurchases	$0.00
Principal Losses	$0.00
Ending Scheduled Principal Balance	$9,639,543.29
INTEREST
Accrued Interest at Gross Rate	$74,260.71
Unscheduled Interest	$0.02
Uncollected Interest	$0.00
Relief Act Shortfall	$0.00
Prepayment Interest Shortfall	$0.00
Other Interest Shortfall	$0.00

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Collateral Report Pool 8043 (Continued)
FEES
Servicing Fees	$3,587.72
Other Fees	$0.00
ADDITIONAL FUNDS
Excess Liquidation Proceeds	$0.00
Subsequent Recoveries	$0.00
Prepayment Penalties	$0.00
Other	$0.00

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Collateral Report Pool 8044
LOAN COUNT
Original Loan Count	1799
Beginning Loan Count	1669
Loans Added	0
Loans Prepaid-in-full	12
Loans Liquidated-in-full	0
Loans Repurchased	0
Ending Loan Count	1657
PRINCIPAL BALANCE
Original Scheduled Principal Balance	$996,941,317.36
Beginning Scheduled Principal Balance	$914,886,195.58
Scheduled Principal Received or Advanced	($3,101,425.26)
Unscheduled Principal	$329,943.58
Prepayments-in-full	$8,113,075.73

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Collateral Report Pool 8044 (Continued)
PRINCIPAL BALANCE
Liquidations-in-full	$0.00
Repurchases	$0.00
Principal Losses	$0.00
Ending Scheduled Principal Balance	$909,544,601.53
INTEREST
Accrued Interest at Gross Rate	$5,856,545.36
Unscheduled Interest	($0.48)
Uncollected Interest	($3,307.88)
Relief Act Shortfall	$0.00
Prepayment Interest Shortfall	$0.00
Other Interest Shortfall	$0.00

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Collateral Report Pool 8044 (Continued)
FEES
Servicing Fees	$956,738.31
Other Fees	$0.00
ADDITIONAL FUNDS
Excess Liquidation Proceeds	$0.00
Subsequent Recoveries	$0.00
Prepayment Penalties	$52,389.97
Other	$0.00

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Collateral Report Group 1
LOAN COUNT
Original Loan Count	1909
Beginning Loan Count	1685
Loans Added	0
Loans Prepaid-in-full	14
Loans Liquidated-in-full	0
Loans Repurchased	0
Ending Loan Count	1671
PRINCIPAL BALANCE
Original Scheduled Principal Balance	$1,100,051,573.81
Beginning Scheduled Principal Balance	$926,366,937.80
Scheduled Principal Received or Advanced	($3,136,007.82)
Unscheduled Principal	$335,163.53
Prepayments-in-full	$9,983,637.27

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Collateral Report Group 1 (Continued)
PRINCIPAL BALANCE
Liquidations-in-full	$0.00
Repurchases	$0.00
Principal Losses	$0.00
Ending Scheduled Principal Balance	$919,184,144.82
INTEREST
Accrued Interest at Gross Rate	$5,930,806.07
Unscheduled Interest	($0.46)
Uncollected Interest	($3,307.88)
Relief Act Shortfall	$0.00
Prepayment Interest Shortfall	$0.00
Other Interest Shortfall	$0.00

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Collateral Report Group 1 (Continued)
FEES
Servicing Fees	$960,326.03
Other Fees	$0.00
ADDITIONAL FUNDS
Excess Liquidation Proceeds	$0.00
Subsequent Recoveries	$0.00
Prepayment Penalties	$52,389.97
Other	$0.00

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Collateral Report Total
LOAN COUNT
Original Loan Count	1909
Beginning Loan Count	1685
Loans Added	0
Loans Prepaid-in-full	14
Loans Liquidated-in-full	0
Loans Repurchased	0
Ending Loan Count	1671
PRINCIPAL BALANCE
Original Scheduled Principal Balance	$1,100,051,573.81
Beginning Scheduled Principal Balance	$926,366,937.80
Scheduled Principal Received or Advanced	($3,136,007.82)
Unscheduled Principal	$335,163.53
Prepayments-in-full	$9,983,637.27

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Collateral Report Total (Continued)
PRINCIPAL BALANCE
Liquidations-in-full	$0.00
Repurchases	$0.00
Principal Losses	$0.00
Ending Scheduled Principal Balance	$919,184,144.82
INTEREST
Accrued Interest at Gross Rate	$5,930,806.07
Unscheduled Interest	($0.46)
Uncollected Interest	($3,307.88)
Relief Act Shortfall	$0.00
Prepayment Interest Shortfall	$0.00
Other Interest Shortfall	$0.00

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Collateral Report Total (Continued)
FEES
Servicing Fees	$960,326.03
Other Fees	$0.00
ADDITIONAL FUNDS
Excess Liquidation Proceeds	$0.00
Subsequent Recoveries	$0.00
Prepayment Penalties	$52,389.97
Other	$0.00

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Delinquency Information by Group*
Group ID	1 Month Count	Scheduled Ending Balance	2 Months Count	Scheduled Ending Balance	3 Months Count	Scheduled Ending Balance	4+ Months Count	Scheduled Ending Balance
Pool 8043	0	$0.00	0	$0.00	0	$0.00	0	$0.00
Pool 8044	33	$17,121,514.89	10	$8,651,184.48	1	$546,538.09	8	$2,451,737.80
Group 1	33	$17,121,514.89	10	$8,651,184.48	1	$546,538.09	8	$2,451,737.80
Aggregate	33	$17,121,514.89	10	$8,651,184.48	1	$546,538.09	8	$2,451,737.80

* Does not include mortgage loans in foreclosure or REO.

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Foreclosure, REO, and Bankruptcy by Group**
Group ID	Foreclosure Count	Scheduled Ending Balance	REO Count	Scheduled Ending Balance	Bankruptcy Count	Scheduled Ending Balance
Pool 8043	0	$0.00	0	$0.00	0	$0.00
Pool 8044	10	$6,404,230.19	1	$2,294,649.59	7	$589,905.71
Group 1	10	$6,404,230.19	1	$2,294,649.59	7	$589,905.71
Aggregate	10	$6,404,230.19	1	$2,294,649.59	7	$589,905.71

** Loans in Bankruptcy will also be reflected under their applicable delinquency or foreclosure status.

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Aggregate Loss Amount by Group
Group ID	Count	Loss Amount
Pool 8043	0	$0.00
Pool 8044	0	$0.00
Group 1	0	$0.00
Aggregate	0	$0.00

Servicer Advances by Group
Group	Count	Total
Pool 8043	13	$28,237.80
Pool 8044	1402	$1,723,575.58
Group 1	1415	$1,751,813.38
Aggregate	1415	$1,751,813.38

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Stop Advances Loans
Group	Count	Loan Balance	Total Scheduled P&I
Pool 8043	0	$0.00	$0.00
Pool 8044	0	$0.00	$0.00
Group 1	0	$0.00	$0.00
Aggregate	0	$0.00	$0.00

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Delinquency Roll Rates-Aggregate***
Current Value	Current		1 Month		2 Months		3 Months
Prior Value	Count	Balance	Count	Balance	Count	Balance	Count	Balance
Current	1596	$874,817,370.80	29	$16,233,211.62	1	$508,786.81	0	$0.00
Delq 1 Month	12	$6,896,918.98	4	$888,303.27	7	$7,043,518.09	0	$0.00
Delq 2 Month	0	$0.00	0	$0.00	2	$1,098,879.58	1	$546,538.09
Delq 3 Month	0	$0.00	0	$0.00	0	$0.00	0	$0.00
Delq 4 Month	0	$0.00	0	$0.00	0	$0.00	0	$0.00
Foreclosure	0	$0.00	0	$0.00	0	$0.00	0	$0.00

Current Value	4+ Months		Foreclosure		REO
Prior Value	Count	Balance	Count	Balance	Count	Balance
Current	0	$0.00	0	$0.00	0	$0.00
Delq 1 Month	0	$0.00	0	$0.00	0	$0.00
Delq 2 Month	0	$0.00	5	$2,389,194.95	0	$0.00
Delq 3 Month	0	$0.00	1	$884,744.28	0	$0.00
Delq 4 Month	2	$1,962,056.32	0	$0.00	0	$0.00
Foreclosure	6	$489,681.48	4	$3,130,290.96	0	$0.00

*** To use this chart, locate along the Current Value row the desired delinquency status as of the immediately preceding due date (e.g. Current, 1 Month delinquent, etc.). Use the left hand column labeled Prior Value to see the prior month's value. Follow the selected Current Value column to the desired Prior Value row.

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Credit Enhancement
Type	Original Balance	Beginning Balance	Reduction	Increase	Ending Balance
Interest Coverage Account	$3,365,583.02	$0.00	$0.00	$0.00	$0.00
Over Collateralization	$0.00	$0.00	$0.00	$0.00	$0.00
Reserve Account	$0.00	$0.00	$0.00	$0.00	$0.00
Other	$0.00	$0.00	$0.00	$0.00	$0.00

Insurance
Insurance Type	Original Balance	Claims Paid	Coverage Remaining
Pool Insurance	$0.00	$0.00	$0.00
Other	$0.00	$0.00	$0.00

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Subordinate Class Certificate Balances
The Class Principal Balances of each Class of the Class B1,B2,B3,B4,B5,B6,B7,B8,B9,B10,B11,B12,B13,B14 Certificates immediately after the principal and interest distribution on 10/25/2007 are as follows:
Class	Ending Principal Balance	Percentage of Aggregate Certificate Principal Balance on Closing Date	Percentage of Aggregate Certificate Ending Principal Balance
B1	$17,025,294.59	1.55%	1.85%
B2	$17,573,466.94	1.60%	1.91%
B3	$5,491,708.42	0.50%	0.60%
B4	$6,590,050.10	0.60%	0.72%
B5	$5,491,708.42	0.50%	0.60%
B6	$4,393,366.72	0.40%	0.48%
B7	$3,844,195.90	0.35%	0.42%
B8	$2,745,854.20	0.25%	0.30%
B9	$4,393,366.72	0.40%	0.48%
B10	$6,040,879.27	0.55%	0.66%
B11	$4,393,366.72	0.40%	0.48%
B12	$2,745,854.20	0.25%	0.30%

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Subordinate Class Certificate Balances
The Class Principal Balances of each Class of the Class B1,B2,B3,B4,B5,B6,B7,B8,B9,B10,B11,B12,B13,B14 Certificates immediately after the principal and interest distribution on 10/25/2007 are as follows:
Class	Ending Principal Balance	Percentage of Aggregate Certificate Principal Balance on Closing Date	Percentage of Aggregate Certificate Ending Principal Balance
B13	$2,745,854.20	0.25%	0.30%
B14	$7,142,689.60	0.65%	0.78%
Total	$90,617,656.00	8.25%	9.86%

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Glossary of Terms
TERM	DEFINITION
Average Ending Scheduled Principal Balance	Average scheduled principal balance of all mortgage loans as of the immediately preceding due date.
Compensating Interest	Interest paid by the servicer or master servicer in respect of Prepayment Interest Shortfall, subject to specified caps.
CPR (Constant Prepayment Rate)	The annualized, compounded single month mortality rate.
Current Interest Accrued	The interest accrued for the current month's distribution.
Deferred Interest	When a scheduled monthly payment is less than required to satisfy the note rate, the unpaid interest is deferred by adding it to the loan balance and the certificate balances.
Excess Liquidation Proceeds	Funds received at the time of liquidation in excess of the amount needed to satisfy the outstanding scheduled principal balance and related expenses.
Interest Rate Accrued	The rate at which interest is accrued for the current month's distribution.
Interest Rate Paid	The rate at which interest is paid for the current month's distribution.
Uncollected Interest	Interest not collected on delinquent loans for which scheduled payments are no longer being advanced, interest uncollected on prepayments and interest uncollected on liquidations.
Other Interest Shortfall	Any interest shortfall other than Uncompensated Interest Shortfall, Deferred Interest or Interest Uncollected on Non-Earning Assets.
Over Collateralization	Any excess of the aggregate principal balance of the mortgage loans over the aggregate principal balance of the certificates.
Prefunding Amount	The amount of cash being held for future loan purchases.

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Glossary of Terms (Continued)
TERM	DEFINITION
Prepayment Interest Shortfall	Any shortfall in collections of interest on mortgage loans resulting from prepayments in full or partial prepayments.
Principal Loss	The amount of principal reduction due to a loss realized on the mortgage loans.
Principal Reimbursed	The amount of principal passed through as a reimbursement.
PSA (Prepayment Speed Assumption)	A prepayment model that in its base case (stated as 100% PSA), assumes that prepayments start in month one at an annual CPR of 0.2%, rising linearly to 6.0% CPR in month 30, and then remain flat at 6.0% CPR thereafter.
Relief Act Shortfall	Interest shortfall resulting from application of the Servicemembers Civil Relief Act.
REO (Real Estate Owned)	Property acquired by the trust through foreclosure or deed-in-lieu of foreclosure on a defaulted loan.
Reserve Account	Funded or non-funded accounts set up at either the property or portfolio level in in anticipation of periodic or non-periodic capital expenditures or cash needs.
Servicer Advances	Scheduled principal and interest advances made by the servicer or master servicer for delinquent mortgage loans.
Servicing Fees	The monthly fee paid to the servicer to perform primary servicing function for the master servicer with respect to the mortgage loans and if applicable the fee charged by the master servicer for supervising the mortgage loan servicing.
SMM (Single Month Mortality)	In any given month, the SMM measures the percentage of the beginning pool balance that was paid back earlier than scheduled through payoffs.
Stop Advance	The amount of principal and interest on delinquent mortgage loans for which scheduled payments are no longer being advanced.
Subsequent Recoveries	The amount of funds recovered on mortgage loans that were previously liquidated at a loss.
Trigger Event	An event that may require a change in payment priority.

Series: WAMU 2007-OA1	Washington Mutual
Issue Date: 01/25/2007
Record Date: 09/28/2007
Distribution Date: 10/25/2007

Glossary of Terms (Continued)
TERM	DEFINITION
Unscheduled Interest	Interested collected in addition to the scheduled interest payment.
Unscheduled Principal	Payments of principal which were received with respect to any mortgage loan during the prior period, other than monthly scheduled principal, prepayments in full, repurchases, liquidation principal and subsequent recoveries.
Weighted Average Loan Age	For any distribution date, the weighted average of the loan age on the mortgage loans as of the immediately preceding due date.
Weighted Average Mortgage Interest Rate	For any distribution date, the weighted average of the mortgage interest rates on the mortgage loans as of the second preceding due date (after giving effect to the payments due on the mortgage loans on that due date).
Weighted Average Pass Through Rate	For any distribution date, the weighted average of the pass-through rates on the mortgage loans as of the second preceding due date (after giving effect to the payments due on the mortgage loans on that due date).
Weighted Average Remaining Term	For any distribution date, the weighted average of the maturity on the mortgage loans as of the immediately preceding due date.
MBA Delinquency Calculation	In this calculation, a loan increases its delinquency status if a monthly payment is not received by the end of the day immediately preceding the loan's next due date.
OTS Delinquency Calculation	In this calculation, a loan increases its delinquency status if a monthly payment is not received by the loan's due date in the following month.

WaMu Mortgage Pass-Through Certificates, Series 2007-OA1 10-D