13D Filing: Oasis Petroleum Inc. and Oasis Midstream Partners LP (OMP)

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

SCHEDULE 13D

(Rule 13d-101)

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO § 240.13d-1(a) AND AMENDMENTS THERETO FILED PURSUANT TO 240.13d-2(a)

UNDER THE SECURITIES EXCHANGE ACT OF 1934

Oasis
Midstream Partners LP

(Name of Issuer)

Common Units Representing Limited Partner Interests

(Title of Class of Securities)

67420T 206

(CUSIP
Number)

Nickolas J. Lorentzatos

1001 Fannin Street, Suite 1500, Houston TX 77002

Tel: (281) 404-9500

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

September 25, 2017

(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 §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following
box.  ☐

Note. Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for
other parties to whom copies are to be sent.

*	The remainder of this cover page shall be filled out for a reporting persons 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).