SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D/A

Under the Securities Exchange Act of 1934

(Amendment No. 1)*

Cimarex Energy Co.

(Name of Issuer)

Common Stock, par value $0.01 per share

(Title of Class of Securities)

171798101

(CUSIP Number)

Robert Atchinson

Adage Capital Partners GP, L.L.C.

200 Clarendon Street, 52nd Floor

Boston, MA 02116

(617) 867-2800

(Name, Address and Telephone Number of Person

Authorized to Receive Notices and Communications)

July 6, 2021

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of Rule 13d-1(e), Rule 13d-1(f) or Rule 13d-1(g), check the following box. [ ]

(Page 1 of 9 Pages)

______________________________

* The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No. 171798101

SCHEDULE 13D/A

Page 2 of 9 Pages

1	NAME OF REPORTING PERSON Adage Capital Partners, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) ¨ (b) ¨
3	SEC USE ONLY
4	SOURCE OF FUNDS WC
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDING IS REQUIRED PURSUANT TO ITEMS 2(d) or 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:	7	SOLE VOTING POWER -0-
	8	SHARED VOTING POWER 6,761,192
	9	SOLE DISPOSITIVE POWER -0-
	10	SHARED DISPOSITIVE POWER 6,761,192
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH PERSON 6,761,192
12	CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES			¨
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 6.58%
14	TYPE OF REPORTING PERSON PN

CUSIP No. 171798101

SCHEDULE 13D/A

Page 3 of 9 Pages

1	NAME OF REPORTING PERSON Adage Capital Partners GP, L.L.C.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) ¨ (b) ¨
3	SEC USE ONLY
4	SOURCE OF FUNDS AF
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDING IS REQUIRED PURSUANT TO ITEMS 2(d) or 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:	7	SOLE VOTING POWER -0-
	8	SHARED VOTING POWER 6,761,192
	9	SOLE DISPOSITIVE POWER -0-
	10	SHARED DISPOSITIVE POWER 6,761,192
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH PERSON 6,761,192
12	CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES			¨
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 6.58%
14	TYPE OF REPORTING PERSON OO

CUSIP No. 171798101

SCHEDULE 13D/A

Page 4 of 9 Pages

1	NAME OF REPORTING PERSON Adage Capital Advisors, L.L.C.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) ¨ (b) ¨
3	SEC USE ONLY
4	SOURCE OF FUNDS AF
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDING IS REQUIRED PURSUANT TO ITEMS 2(d) or 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:	7	SOLE VOTING POWER -0-
	8	SHARED VOTING POWER 6,761,192
	9	SOLE DISPOSITIVE POWER -0-
	10	SHARED DISPOSITIVE POWER 6,761,192
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH PERSON 6,761,192
12	CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES			¨
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 6.58%
14	TYPE OF REPORTING PERSON OO

CUSIP No. 171798101

SCHEDULE 13D/A

Page 5 of 9 Pages

1	NAME OF REPORTING PERSON Robert Atchinson
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) ¨ (b) ¨
3	SEC USE ONLY
4	SOURCE OF FUNDS AF
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDING IS REQUIRED PURSUANT TO ITEMS 2(d) or 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION United States
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:	7	SOLE VOTING POWER -0-
	8	SHARED VOTING POWER 6,761,192
	9	SOLE DISPOSITIVE POWER -0-
	10	SHARED DISPOSITIVE POWER 6,761,192
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH PERSON 6,761,192
12	CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES			¨
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 6.58%
14	TYPE OF REPORTING PERSON IN

CUSIP No. 171798101

SCHEDULE 13D/A

Page 6 of 9 Pages

1	NAME OF REPORTING PERSON Phillip Gross
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) ¨ (b) ¨
3	SEC USE ONLY
4	SOURCE OF FUNDS AF
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDING IS REQUIRED PURSUANT TO ITEMS 2(d) or 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION United States
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:	7	SOLE VOTING POWER -0-
	8	SHARED VOTING POWER 6,761,192
	9	SOLE DISPOSITIVE POWER -0-
	10	SHARED DISPOSITIVE POWER 6,761,192
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH PERSON 6,761,192
12	CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES			¨
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 6.58%
14	TYPE OF REPORTING PERSON IN

CUSIP No. 171798101

SCHEDULE 13D/A

Page 7 of 9 Pages

This Amendment No. 1 (“Amendment No. 1”) amends and supplements the statement on Schedule 13D filed with the Securities and Exchange Commission (the “SEC”) on June 14, 2021 (the “Original Schedule 13D” and together with this Amendment No. 1, the “Schedule 13D”) with respect to the shares of Common Stock, $0.01 par value per share (the “Common Stock”), of Cimarex Energy Co., a Delaware corporation (the “Issuer”). This Amendment No. 1 amends Items 3 and 5 as set forth below.


Item 3.	SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION
	Item 3 of the Schedule 13D is hereby amended and restated as follows:
	Funds for the purchase of the 6,761,192 shares of Common Stock to which this Schedule 13D relates were derived from working capital of ACP made in the ordinary course of business. A total of $447,516,415.63 was paid to acquire the 6,761,192 shares of Common Stock reported herein. ACPGP, ACA and Messrs. Atchinson or Gross control the investing and trading in securities of ACP. None of ACPGP, ACA or Messrs. Atchinson or Gross directly hold any shares of Common Stock.

Item 5.	INTEREST IN SECURITIES OF THE ISSUER
	Item 5 of the Schedule 13D is hereby amended and restated as follows:
(a)	See rows (11) and (13) of the cover pages to this Schedule 13D for the aggregate number of shares of Common Stock and percentages of the shares of Common Stock beneficially owned by each of the Reporting Persons. The percentages used in this Schedule 13D are calculated based upon 102,825,296 shares of Common Stock outstanding on May 21, 2021, as disclosed in the Merger Agreement attached as Exhibit 2.1 to the Company’s Current Report on Form 8-K filed with the Securities and Exchange Commission on May 24, 2021.

(b)	See rows (7) through (10) of the cover pages to this Schedule 13D for the number of shares of Common Stock as to which each Reporting Person has the sole or shared power to vote or direct the vote and sole or shared power to dispose or to direct the disposition.

(c)	The transactions in the shares of Common Stock since the filing of the Original schedule 13D by ACP, which were all in the open market, are set forth in Schedule A, and are incorporated herein by reference. The other Reporting Persons did not enter into any transactions in the shares of Common Stock since the filing of the Original schedule 13D.

(d)	No person other than the Reporting Persons is known to have the right to receive, or the power to direct the receipt of dividends from, or proceeds from the sale of, such shares of Common Stock.

(e)	Not applicable.

CUSIP No. 171798101

SCHEDULE 13D/A

Page 8 of 9 Pages

SIGNATURES

After reasonable inquiry and to the best of his or its knowledge and belief, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.

Date: July 8, 2021



ADAGE CAPITAL PARTNERS, L.P.
By: Adage Capital Partners GP, L.L.C.,
its general partner

By: Adage Capital Advisors, L.L.C.,
its managing member

/s/ Robert Atchinson
Name: Robert Atchinson
Title: Managing Member

ADAGE CAPITAL PARTNERS GP, L.L.C.
By: Adage Capital Advisors, L.L.C.,
its managing member

/s/ Robert Atchinson
Name: Robert Atchinson
Title: Managing Member

ADAGE CAPITAL ADVISORS, L.L.C.

/s/ Robert Atchinson
Name: Robert Atchinson
Title: Managing Member

/s/ Robert Atchinson
ROBERT ATCHINSON, individually

/s/ Phillip Gross
PHILLIP GROSS, individually

CUSIP No. 171798101

SCHEDULE 13D/A

Page 9 of 9 Pages

Schedule A

This Schedule sets forth information with respect to each purchase and sale of shares of Common Stock which were effectuated by ACP since the filing of the Original schedule 13D. All transactions were effectuated in the open market through a broker. The price reported in the column Price Per Share ($) is a weighted average price if a price range is indicated in the column Price Range ($). These shares of Common Stock were purchased/sold in multiple transactions at prices between the price ranges below. The Reporting Persons will undertake to provide to the staff of the SEC, upon request, full information regarding the number of shares of Common Stock sold at each separate price.

Trade Date	Shares Purchased (Sold)	Price Per Share ($)*	Price Range ($)*
06/15/2021	110,000	69.7072	69.6224-70.2650
06/16/2021	100,000	69.8028	69.8013-69.9078
06/17/2021	100,000	65.8274	65.8196-65.8316
06/18/2021	100,000	64.8239	64.8220-64.8314
06/24/2021	100,000	71.2671
06/25/2021	11,849	70.4588
06/28/2021	88,151	70.2941	69.8714-70.3317
06/29/2021	12,798	71.3224
06/30/2021	87,202	71.5367
07/01/2021	148,887	74.0417	73.9092-74.1045
07/02/2021	161,213	73.9894	73.6600-74.1400
07/06/2021	224,900	71.3615	71.2870-71.8263
07/07/2021	50,000	70.6363	70.5404-70.7342
07/08/2021	71,071	70.7651
07/08/2021	100,000	72.6256	72.6800-72.8950

* Excluding commissions.

CIMAREX ENERGY CO SC 13D/A