X0306 4 2021-03-19 0 0001652133 Oasis Midstream Partners LP OMP 0001486159 Oasis Petroleum Inc. 1001 FANNIN ST., SUITE 1500 HOUSTON TX 77002 0 0 1 0 0001494070 Oasis Petroleum LLC 1001 FANNIN STREET, SUITE 1500 HOUSTON TX 77002 0 0 1 0 0001717320 OMS Holdings LLC 1001 FANNIN STREET, SUITE 1500 HOUSTON TX 77002 0 0 1 0 Common units representing limited partner interests 2021-03-19 4 C 0 13750000 A 22825000 I See Footnotes Subordinated units representing limited partner interests 2021-03-19 4 C 0 13750000 D Common units representing limited partner interests 13750000 0 I See Footnotes On March 19, 2021, upon satisfaction of certain financial conditions for the conversion of the subordinated units representing limited partner interests of the Issuer ("Subordinated Units") set forth in the Issuer's Amended and Restated Agreement of Limited Partnership (the "Agreement"), all of the outstanding Subordinated Units automatically converted into common units representing limited partner interests of the Issuer (the "Common Units") on a one-for-one basis, pursuant to the terms of the Agreement, for no additional consideration. Upon the conversion of all of the Subordinated Units to Common Units, the Subordination Period (as defined in the Agreement) automatically terminated. This Form 4 is being jointly filed by OMS Holdings LLC ("OMS Holdings"), Oasis Petroleum LLC ("Oasis Petroleum") and Oasis Petroleum Inc. ("OAS"). As of March 19, 2021, OMS Holdings directly owns 22,825,000 common units, Oasis Petroleum directly owns 100% of the outstanding membership interests in OMS Holdings and OAS directly owns 100% of the outstanding membership interests in Oasis Petroleum. Accordingly, OAS and Oasis Petroleum may be deemed to be an indirect beneficial owner of the securities of the Issuer held by OMS Holdings. /s/ Nickolas J. Lorentzatos, Executive Vice President, General Counsel and Corporate Secretary of Oasis Petroleum Inc. 2021-03-19 /s/ Nickolas J. Lorentzatos, Executive Vice President, General Counsel and Corporate Secretary of Oasis Petroleum LLC 2021-03-19 /s/ Nickolas J. Lorentzatos, Executive Vice President, General Counsel and Corporate Secretary of OMS Holdings LLC 2021-03-19