SC 13G

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

(Amendment No.     )*

Oasis Petroleum Inc.

(Name of Issuer)

COMMON STOCK

(Title of Class of Securities)

674215108

(CUSIP Number)

June 13, 2011

(Date of Event which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

¨ Rule 13d-1(b)

x Rule 13d-1(c)

¨ Rule 13d-1(d)

* 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).

Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number.

CUSIP No. 674215108

1.	Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only). SPO Partners II, L.P.
2.	Check the Appropriate Box if a Member of a Group (See Instructions) (a)  ¨        (b)  x
3.	SEC Use Only
4.	Citizenship or Place of Organization     Delaware
Number of Shares Beneficially Owned by Each Reporting Person With:		5.	Sole Voting Power      6,199,259(1)
		6.	Shared Voting Power     0
		7.	Sole Dispositive Power     6,199,259(1)
		8.	Shared Dispositive Power     0
9.	Aggregate Amount Beneficially Owned by Each Reporting Person      6,199,259
10.	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)    ¨
11.	Percent of Class Represented by Amount in Row (9)     6.7%
12.	Type of Reporting Person (See Instructions)     (PN)

(1) Power is exercised through its sole general partner, SPO Advisory Partners, L.P.

Page 2 of 13

CUSIP No. 674215108

1.	Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only). SPO Advisory Partners, L.P.
2.	Check the Appropriate Box if a Member of a Group (See Instructions) (a)  ¨        (b)  x
3.	SEC Use Only
4.	Citizenship or Place of Organization     Delaware
Number of Shares Beneficially Owned by Each Reporting Person With:		5.	Sole Voting Power      6,199,259 (1)(2)
		6.	Shared Voting Power     0
		7.	Sole Dispositive Power      6,199,259 (1)(2)
		8.	Shared Dispositive Power     0
9.	Aggregate Amount Beneficially Owned by Each Reporting Person      6,199,259
10.	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)    ¨
11.	Percent of Class Represented by Amount in Row (9)     6.7%
12.	Type of Reporting Person (See Instructions)     (PN)

(1) Solely in its capacity as the sole general partner of SPO Partners II, L.P.

(2) Power is exercised through its sole general partner, SPO Advisory Corp.

Page 3 of 13

CUSIP No. 674215108

1.	Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only). San Francisco Partners, L.P.
2.	Check the Appropriate Box if a Member of a Group (See Instructions) (a)  ¨        (b)  x
3.	SEC Use Only
4.	Citizenship or Place of Organization      California
Number of Shares Beneficially Owned by Each Reporting Person With:		5.	Sole Voting Power      182,900(1)
		6.	Shared Voting Power     0
		7.	Sole Dispositive Power      182,900(1)
		8.	Shared Dispositive Power     0
9.	Aggregate Amount Beneficially Owned by Each Reporting Person      182,900
10.	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)    ¨
11.	Percent of Class Represented by Amount in Row (9)      0.2%
12.	Type of Reporting Person (See Instructions)      (PN)

(1) Power is exercised through its sole general partner, SF Advisory Partners, L.P.

Page 4 of 13

CUSIP No. 674215108

1.	Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only). SF Advisory Partners, L.P.
2.	Check the Appropriate Box if a Member of a Group (See Instructions) (a)  ¨        (b)  x
3.	SEC Use Only
4.	Citizenship or Place of Organization     Delaware
Number of Shares Beneficially Owned by Each Reporting Person With:		5.	Sole Voting Power      182,900(1)(2)
		6.	Shared Voting Power     0
		7.	Sole Dispositive Power     182,900(1)(2)
		8.	Shared Dispositive Power     0
9.	Aggregate Amount Beneficially Owned by Each Reporting Person      182,900
10.	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)    ¨
11.	Percent of Class Represented by Amount in Row (9)     0.2%
12.	Type of Reporting Person (See Instructions)     (PN)

(1) Solely in its capacity as the sole general partner of San Francisco Partners, L.P.

(2) Power is exercised through its sole general partner, SPO Advisory Corp.

Page 5 of 13

CUSIP No. 674215108

1.	Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only). SPO Advisory Corp.
2.	Check the Appropriate Box if a Member of a Group (See Instructions) (a)  ¨        (b)  x
3.	SEC Use Only
4.	Citizenship or Place of Organization     Delaware
Number of Shares Beneficially Owned by Each Reporting Person With:		5.	Sole Voting Power      6,382,159(1)(2)
		6.	Shared Voting Power     0
		7.	Sole Dispositive Power     6,382,159(1)(2)
		8.	Shared Dispositive Power     0
9.	Aggregate Amount Beneficially Owned by Each Reporting Person      6,382,159
10.	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)    ¨
11.	Percent of Class Represented by Amount in Row (9)     6.9%
12.	Type of Reporting Person (See Instructions)     (CO)

(1) Solely in its capacity as the sole general partner of SPO Advisory Partners, L.P. with respect to 6,199,259 of such shares; and solely in its capacity as the sole general partner of SF Advisory Partners, L.P. with respect to 182,900 of such shares.

(2) Power is exercised through its three controlling persons, John H. Scully, William E. Oberndorf and Edward H. McDermott.

Page 6 of 13

CUSIP No. 674215108

1.	Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only). John H. Scully
2.	Check the Appropriate Box if a Member of a Group (See Instructions) (a)  ¨        (b)  x
3.	SEC Use Only
4.	Citizenship or Place of Organization     USA
Number of Shares Beneficially Owned by Each Reporting Person With:		5.	Sole Voting Power      9,400(1)
		6.	Shared Voting Power     6,382,159(2)
		7.	Sole Dispositive Power     9,400(1)
		8.	Shared Dispositive Power     6,382,159(2)
9.	Aggregate Amount Beneficially Owned by Each Reporting Person      6,391,559
10.	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)    ¨
11.	Percent of Class Represented by Amount in Row (9)     6.9%
12.	Type of Reporting Person (See Instructions)     (IN)

(1) These shares are held in Mr. Scully’s Individual Retirement Account, which is self-directed.

(2) These shares may be deemed to be beneficially owned by Mr. Scully solely in his capacity as one of three controlling persons of SPO Advisory Corp.

Page 7 of 13

CUSIP No. 674215108

1.	Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only). William E. Oberndorf
2.	Check the Appropriate Box if a Member of a Group (See Instructions) (a)  ¨        (b)  x
3.	SEC Use Only
4.	Citizenship or Place of Organization     USA
Number of Shares Beneficially Owned by Each Reporting Person With:		5.	Sole Voting Power      29,700(1)
		6.	Shared Voting Power     6,382,159(2)
		7.	Sole Dispositive Power     29,700(1)
		8.	Shared Dispositive Power     6,382,159(2)
9.	Aggregate Amount Beneficially Owned by Each Reporting Person      6,411,859
10.	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)    ¨
11.	Percent of Class Represented by Amount in Row (9)     6.9%
12.	Type of Reporting Person (See Instructions)     (IN)

(1) These shares are held in Mr. Oberndorf’s Individual Retirement Account, which is self-directed.

(2) These shares may be deemed to be beneficially owned by Mr. Oberndorf solely in his capacity as one of three controlling persons of SPO Advisory Corp.

Page 8 of 13

CUSIP No. 674215108

1.	Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only). Edward H. McDermott
2.	Check the Appropriate Box if a Member of a Group (See Instructions) (a)  ¨        (b)  x
3.	SEC Use Only
4.	Citizenship or Place of Organization     USA
Number of Shares Beneficially Owned by Each Reporting Person With:		5.	Sole Voting Power      500(1)
		6.	Shared Voting Power     6,382,159(2)
		7.	Sole Dispositive Power     500(1)
		8.	Shared Dispositive Power     6,382,159(2)
9.	Aggregate Amount Beneficially Owned by Each Reporting Person      6,382,659
10.	Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)    ¨
11.	Percent of Class Represented by Amount in Row (9)     6.9%
12.	Type of Reporting Person (See Instructions)     (IN)

(1) These shares are held in Mr. McDermott’s Individual Retirement Account, which is self-directed.

(2) These shares may be deemed to be beneficially owned by Mr. McDermott solely in his capacity as one of three controlling persons of SPO Advisory Corp.

Page 9 of 13

Item 1.	(a)	Name of Issuer
		Oasis Petroleum Inc.
	(b)	Address of Issuer’s Principal Executive Offices
		1001 Fannin Street, Suite 1500 Houston, Texas 77002
Item 2.	(a)	Name of Person Filing
		SPO Partners II, L.P., a Delaware limited partnership (“SPO”), SPO Advisory Partners, L.P., a Delaware limited partnership (“SPO Advisory Partners”), San Francisco Partners, L.P., a California limited partnership (“SFP”), SF Advisory Partners, L.P., a Delaware limited partnership (“SF Advisory Partners”), SPO Advisory Corp., a Delaware corporation (“SPO Advisory Corp.”), John H. Scully (“JHS”), William E. Oberndorf (“WEO”) and Edward H. McDermott (“EHM”). SPO, SPO Advisory Partners, SFP, SF Advisory Partners, SPO Advisory Corp., JHS, WEO and EHM are sometimes hereinafter referred to as the “Reporting Persons.” The Reporting Persons are making this single, joint filing because they may be deemed to constitute a “group” within the meaning of Section 13(d)(3) of the Securities Exchange Act of 1934, as amended (the “Act”), although neither the fact of this filing nor anything contained herein shall be deemed to be an admission by the Reporting Persons that a group exists.
	(b), (c)	Address of Principal Business Office or, if None, Residence; Citizenship of Reporting Persons
		The principal business address of SPO is 591 Redwood Highway, Suite 3215, Mill Valley, California 94941. SPO is a Delaware limited partnership. The principal business address of SPO Advisory Partners is 591 Redwood Highway, Suite 3215, Mill Valley, California 94941. SPO Advisory Partners is a Delaware limited partnership. The principal business address of SFP is 591 Redwood Highway, Suite 3215, Mill Valley, California 94941. SFP is a California limited partnership.
		The principal business address of SF Advisory Partners is 591 Redwood Highway, Suite 3215, Mill Valley, California 94941. SF Advisory Partners is a Delaware limited partnership. The principal business address of SPO Advisory Corp. is 591 Redwood Highway, Suite 3215, Mill Valley, California 94941. SPO Advisory Corp. is a Delaware corporation. The principal business address of JHS is 591 Redwood Highway, Suite 3215, Mill Valley, California 94941. JHS is a citizen of the United States of America. The principal business address of WEO is 591 Redwood Highway, Suite 3215, Mill Valley, California 94941. WEO is a citizen of the United States of America.
		The principal business address of EHM is 591 Redwood Highway, Suite 3215, Mill Valley, California 94941. EHM is a citizen of the United States of America.
	(d)	Title of Class of Securities
		Common Stock, par value $0.01 per share.
	(e)	CUSIP Number:
		674215108
Item 3.	Statement filed pursuant to §§240.13d-1(b) or 240.13d-2(b) or (c):
	Not Applicable.
Item 4.	Ownership.
	Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

Page 10 of 13

	(b)			(a)		(c)(i)		(c)(ii)		(c)(iii)		(c)(iv)
				Common Shares
						Voting Power				Disposition Power
Reporting Persons	Percent of Class			Beneficially Owned		Sole		Shared		Sole		Shared
SPO Partners II, L.P.		6.7	%		6,199,259		6,199,259		0		6,199,259		0
SPO Advisory Partners, L.P.		6.7	%		6,199,259		6,199,259		0		6,199,259		0
San Francisco Partners, L.P.		0.2	%		182,900		182,900		0		182,900		0
SF Advisory Partners, L.P.		0.2	%		182,900		182,900		0		182,900		0
SPO Advisory Corp.		6.9	%		6,382,159		6,382,159		0		6,382,159		0
John H. Scully		6.9	%		6,391,559		9,400		6,382,159		9,400		6,382,159
William E. Oberndorf		6.9	%		6,411,859		29,700		6,382,159		29,700		6,382,159
Edward H. McDermott		6.9	%		6,382,659		500		6,382,159		500		6,382,159

** Denotes less than

	Instruction. For computations regarding securities which represent a right to acquire an underlying security see §240.13d-3(d)(1).
Item 5.	Ownership of Five Percent or Less of a Class.
	If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following  ¨.
Item 6.	Ownership of More than Five Percent on Behalf of Another Person.
	No other persons have the right to receive or the power to direct the receipt of dividends from, or the proceeds from, or other proceeds from the sale of, the common shares held by the Reporting Persons.
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable.
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable.
Item 9.	Notice of Dissolution of Group.
	Not Applicable.
Item 10.	Certification.
	By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

Page 11 of 13

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

June 23, 2011

Date

/s/ Kim M. Silva

Signature

Kim M. Silva

Attorney-in-fact for:

SPO Partners II, L.P. (1)

SPO Advisory Partners, L.P. (1)

San Francisco Partners, L.P. (1)

SF Advisory Partners, L.P. (1)

SPO Advisory Corp. (1)

John H. Scully (1)

William E. Oberndorf (1)

Edward H. McDermott (1)

(1) A Power of Attorney authorizing Kim M. Silva to act on behalf of this person or entity is filed as Exhibit B.

Page 12 of 13

EXHIBIT INDEX

Exhibit	Document Description
A	Agreement Pursuant to Rule 13d-1(k)
B	Power of Attorney

Page 13 of 13

EX-99.A

EXHIBIT A

Pursuant to Rule 13d-1(k) or Regulation 13D-G of the General Rule and Regulations of the Securities and Exchange Commission under the Securities Exchange Act of 1934, as amended, the undersigned agrees that the statement to which this Exhibit is attached is filed on behalf of each of them in capacities set forth below.

June 23, 2011

Date

/s/ Kim M. Silva

Signature

Kim M. Silva

Attorney-in-fact for:

SPO Partners II, L.P. (1)

SPO Advisory Partners, L.P. (1)

San Francisco Partners, L.P. (1)

SF Advisory Partners, L.P. (1)

SPO Advisory Corp. (1)

John H. Scully (1)

William E. Oberndorf (1)

Edward H. McDermott (1)

(1) A Power of Attorney authorizing Kim M. Silva to act on behalf of this person or entity is filed as Exhibit B.

EX-99.B

EXHIBIT B

POWER OF ATTORNEY

KNOW ALL PERSONS BY THESE PRESENTS, that each of SPO Partners II, L.P., SPO Advisory Partners, L.P., San Francisco Partners, L.P., SF Advisory Partners, L.P., SPO Advisory Corp., John H. Scully, William E. Oberndorf and Edward H. McDermott (each, a “Grantor”) has made, constituted and appointed, and by these presents does make, constitute and appoint, each of William E. Oberndorf and Kim M. Silva (each an “Attorney”), the true and lawful agent and attorney-in-fact, with full power of substitution and resubstitution, of the Grantor, for and in Grantor’s name, place and stead, in any and all capacities, to do all or any of the following acts, matters and things:

1. To sign on behalf of the Grantor statements on Schedule 13D or 13G or Forms 3, 4 and 5, or amendments thereto pursuant to Section 13(d) or Section 16 under the Securities Exchange Act of 1934.

2. To do all such other acts and things as, in such Attorney’s discretion, he or she deems appropriate or desirable for the purpose of filing such statements on Schedule 13D or 13G or Forms 3, 4 and 5, or amendments thereto.

3. To appoint in writing one or more substitutes who shall have the power to act on behalf of the Grantor as if that substitute or those substitutes shall have been originally appointed Attorney(s) by this Power of Attorney and/or to revoke any such appointment at any time without assigning any reason therefor.

The Grantor hereby ratifies and confirms all that said agents and attorneys-in-fact or any substitute or substitutes may lawfully do or cause to be done by virtue hereof. This power of Attorney shall remain in full force and effect until the undersigned is no longer required to file Forms 3, 4 and 5 or to file reports under Section 13(d) of the Securities Exchange Act of 1934 with respect to the undersigned’s holdings of and transactions in securities issued by Oasis Petroleum Inc., unless earlier revoked by the undersigned in a signed writing delivered to the foregoing attorneys-in-fact.

The words Grantor and Attorney shall include all grantors and attorneys under this Power of Attorney.

IN WITNESS WHEREOF, Grantor duly assents to this Power of Attorney by his, her or its signature as of the 23rd of June, 2011

SPO Partners II, L.P.

/s/ SPO Partners II, L.P.

SPO Advisory Partners, L.P.

/s/ SPO Advisory Partners, L.P.

San Francisco Partners, L.P.

/s/ San Francisco Partners, L.P.

SF Advisory Partners, L.P.

/s/ SF Advisory Partners, L.P.

SPO Advisory Corp.

/s/ SPO Advisory Corp.

John H. Scully

/s/ John H. Scully

William E. Oberndorf

/s/ William E. Oberndorf

Edward H. McDermott

/s/ Edward H. McDermott