| 1 | O G & E | Oklahoma City, OK 73124 | Oil & Gas Operator | Feb 2014 |
| 2 | O K Swabbing Inc | Hennessey, OK 73742 | Oil & Gas Operator | Sep 2024 |
| 3 | Oexco, Inc. | Tulsa, OK 74136 | Oil & Gas Operator | Mar 2015 |
| 4 | Ofs-Tulsa Corporation | Fort Worth, TX 76102 | Oil & Gas Operator | Feb 1997 |
| 5 | Oil Producers, Inc. Of Kansas | Wichita, KS 67206 | Oil & Gas Operator | Dec 2024 |
| 6 | Oilfield Operating Company | Cushing, OK 74023-1347 | Oil & Gas Operator | Jan 2018 |
| 7 | Oilsearch Corporation | Albuquerque, NM 87109 | Oil & Gas Operator | Feb 1994 |
| 8 | Okie Crude Company | Tulsa, OK 74103 | Oil & Gas Operator | Sep 2024 |
| 9 | Oklahoma Equipment & Salvage | Oklahoma City, OK 73120-5903 | Oil & Gas Operator | Mar 2015 |
| 10 | Oklahoma Oil & Gas MGMT Inc | Edmond, OK 73083-6786 | Oil & Gas Operator | Oct 2024 |
| 11 | Oklahoma Oil Tactics Inc | Edmond, OK 73003-1351 | Oil & Gas Operator | Mar 2015 |
| 12 | Okland Oil Company | Oklahoma City, OK 73102-9022 | Oil & Gas Operator | Oct 2024 |
| 13 | Okt Petroleum Company Inc | Oklahoma City, OK 73118-7425 | Oil & Gas Operator | Oct 2013 |
| 14 | Omimex International Corporation | Fort Worth, TX 76103-2300 | Oil & Gas Operator | Sep 2024 |
| 15 | Oneok Field Services Company | Tulsa, OK 74103 | Oil & Gas Operator | Jul 2022 |
| 16 | Oneok Resources Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 17 | Onyx Energy Corporation | Oklahoma City, OK 73157 | Oil & Gas Operator | May 1994 |
| 18 | Onyx Properties Corp | Oklahoma City, OK 73114 | Oil & Gas Operator | May 2006 |
| 19 | Opal Operating Company LLC | Oklahoma City, OK 73142 | Oil & Gas Operator | Dec 2024 |
| 20 | Opubco Resources Of TX Inc | Dallas, TX 75231 | Oil & Gas Operator | Sep 2005 |
| 21 | Orca Operating Company LLC | Houston, TX 77056 | Oil & Gas Operator | Oct 2024 |
| 22 | Otc Petroleum Corporation | Nichols Hill, OK 73116 | Oil & Gas Operator | Mar 2015 |
| 23 | Overflow Energy Stack LLC | Booker, TX 79005 | Oil Operator | Sep 2022 |
| 24 | Overflow Energy, LLC | Booker, TX 79005 | Oil & Gas Operator | Dec 2024 |
| 25 | Ovintiv Mid-Continent Inc. | The Woodlands, TX 77380-2764 | Oil & Gas Operator | Oct 2024 |
| 26 | Ovintiv USA Inc. | Denver, CO 80202 | Oil & Gas Operator | Dec 2024 |
| 27 | Oxy USA Inc | Houston, TX 77046 | Oil & Gas Operator | Dec 2024 |