Insider · CIK 0001218663

OBERNDORF WILLIAM E

Reports to the SEC for 14 companies · MILL VALLEY, CA

sec.gov

Transactions

Companies

Filings

CIK

0001218663

Summary

William E. Oberndorf

Updated Dec 21, 2025

William E. Oberndorf is an investor and founder of SPO Partners who has acted as a controlling person of investment vehicles that file institutional investor disclosures with the SEC. Public filings record his substantial, disclosed holdings and director-level relationships with several publicly traded companies.^[1]

Career Background

Founded and led investment vehicles (SPO Partners and related entities) that file Form 13F and Schedule 13D/G disclosures as institutional investors.^[1]
Served in board and investor roles across multiple companies, with public biographies and filings naming Calpine and other corporate directorships.^[2]
Participated as a controlling person in SPO Advisory / SPO Partners groups that have appeared as reporting persons in issuer filings and proxy materials.^[3]

Current Positions

Significant shareholder / reporting person associated with SPO Advisory / SPO Partners — reflected in SEC institutional and Section 16 filings.^[1]
Identified in public company filings and proxy statements as a disclosed investor or board-affiliated reporting person for issuers such as Cabot Corporation (CBT) and Calpine Corporation (CPN).^[3]

SEC Filing Context

Files and appears as a reporting person in Form 13F institutional holdings reports and in Section 16 filings (Forms 3/4) submitted to the SEC, indicating sustained institutional investment activity.^[1]

Forms 4 and 5

Insider transactions

21 trades

Date	Company	Role	Code	Shares	Price	Value	Shares after
2017-06-19	APPFAPPFOLIO INCS Sale	Former 10% Owner	SSale	−220K sh	$31.25	−$6.88M	286,171
2017-05-09	APPFAPPFOLIO INCS Sale	Former 10% Owner	SSale	−3,250 sh	$27.00	−$87.8K	850
2017-03-22	APPFAPPFOLIO INCS Sale	Former 10% Owner	SSale	−35.2K sh	$24.07	−$847K	10,700
2017-03-22	APPFAPPFOLIO INCS Sale	Former 10% Owner	SSale	−300 sh	$24.07	−$7,221	30
2017-03-22	APPFAPPFOLIO INCS Sale	Former 10% Owner	SSale	−4,500 sh	$24.07	−$108K	8,612
2017-03-07	APPFAPPFOLIO INCJ Other	Former 10% Owner	JOther	−2,000 sh	—	—	631,086
2017-03-03	APPFAPPFOLIO INCS Sale	Former 10% Owner	SSale	−500K sh	$23.25	−$11.6M	185,269
2015-10-06	APPFAPPFOLIO INCP Purchase	Former 10% Owner	PPurchase	+667K sh	$16.50	+$11M	1,135,567
2015-07-09	APPFAPPFOLIO INCP Purchase	Former 10% Owner	PPurchase	+4,800 sh	$13.99	+$67.2K	468,900
2015-07-07	APPFAPPFOLIO INCP Purchase	Former 10% Owner	PPurchase	+8,000 sh	$13.83	+$111K	464,100
2015-07-06	APPFAPPFOLIO INCP Purchase	Former 10% Owner	PPurchase	+1,600 sh	$13.90	+$22.2K	456,100
2015-07-02	APPFAPPFOLIO INCP Purchase	Former 10% Owner	PPurchase	+7,500 sh	$13.96	+$105K	454,500
2012-05-15	CALPINE CORPA Award	Director	AAward	+5,166 sh	—	—	39,317
2012-03-31	LAMRLAMAR ADVERTISING CO/NEWS Sale	10% Owner	SSale	0 sh	—	—	18,723,314
2012-03-31	CHRDChord Energy CorpS Sale	10% Owner	SSale	0 sh	—	—	9,566,749
2012-03-31	PETROQUEST ENERGY INCS Sale	10% Owner	SSale	0 sh	—	—	7,873,184
2012-03-31	Cimarex Resolute LLCS Sale	10% Owner	SSale	0 sh	—	—	9,915,610
2012-03-31	CALPINE CORPS Sale	Director	SSale	0 sh	—	—	77,501,208
2012-03-31	ADVENT SOFTWARE INC /DE/S Sale	10% Owner	SSale	0 sh	—	—	15,712,200
2012-03-31	QUICKSILVER RESOURCES INCS Sale	10% Owner	SSale	0 sh	—	—	25,140,554
2011-05-11	CALPINE CORPA Award	Director	AAward	+5,451 sh	—	—	93,999,691

Recent filings

Accepted (ET)
Jun 214
APPFOLIO INC0000899243-17-016877
SEC(opens sec.gov)
May 114
APPFOLIO INC0000899243-17-012883
SEC(opens sec.gov)
Mar 244
APPFOLIO INC0000899243-17-008549
SEC(opens sec.gov)
Mar 74
APPFOLIO INC0000899243-17-006716
SEC(opens sec.gov)
Oct 84
APPFOLIO INC0000899243-15-006452
SEC(opens sec.gov)
Jul 134
APPFOLIO INC0000899243-15-001087
SEC(opens sec.gov)
Jul 94
APPFOLIO INC0000899243-15-000945
SEC(opens sec.gov)
Jul 74
APPFOLIO INC0000899243-15-000787
SEC(opens sec.gov)
May 174
OBERNDORF WILLIAM E0001140361-12-026080
SEC(opens sec.gov)
Apr 24
WILLIAM & SUSAN OBERNDORF TRUST0001181431-12-021305
SEC(opens sec.gov)
Apr 24
WILLIAM & SUSAN OBERNDORF TRUST0001181431-12-021302
SEC(opens sec.gov)
Apr 24
WILLIAM & SUSAN OBERNDORF TRUST0001181431-12-021303
SEC(opens sec.gov)
Apr 24
WILLIAM & SUSAN OBERNDORF TRUST0001181431-12-021304
SEC(opens sec.gov)
Apr 24
WILLIAM & SUSAN OBERNDORF TRUST0001181431-12-021297
SEC(opens sec.gov)
Apr 24
SCULLY JOHN H0001181431-12-021292
SEC(opens sec.gov)
Apr 24
WILLIAM & SUSAN OBERNDORF TRUST0001181431-12-021300
SEC(opens sec.gov)

Companies

Address

591 REDWOOD HIGHWAY, SUITE 3215

MILL VALLEY, CA, 94941