| 1 | O G & E | Oklahoma City, OK 73124 | Oil & Gas Operator | Feb 2014 |
| 2 | O K Swabbing Inc | Hennessey, OK 73742 | Oil & Gas Operator | Jul 2025 |
| 3 | O'Neill Properties, LTD. | Midland, TX 79702 | Oil & Gas Operator | Oct 2025 |
| 4 | Oak Resources Inc | Tulsa, OK 74153 | Oil & Gas Operator | Aug 2013 |
| 5 | Oil Producers, Inc. Of Kansas | Wichita, KS 67206 | Oil & Gas Operator | Oct 2025 |
| 6 | Oilsearch Corporation | Albuquerque, NM 87109 | Oil & Gas Operator | Feb 1994 |
| 7 | Okie Crude Company | Tulsa, OK 74103 | Oil & Gas Operator | Jun 2025 |
| 8 | Oklahoma Oil & Gas MGMT Inc | Edmond, OK 73083-6786 | Oil & Gas Operator | Jun 2025 |
| 9 | Okland Oil Company | Oklahoma City, OK 73102-9022 | Oil & Gas Operator | Jul 2025 |
| 10 | Old Dominion Oil Corporation | Oklahoma City, OK 73107 | Oil & Gas Operator | Apr 2009 |
| 11 | Olympia Oil Inc | Edmond, OK 73083-7088 | Oil & Gas Operator | Jul 2020 |
| 12 | Omimex International Corporation | Fort Worth, TX 76103-2300 | Oil & Gas Operator | Jun 2025 |
| 13 | Oneok Exploration Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 14 | Oneok Resources Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 15 | Onshore Royalties LLC | Houston, TX 77269 | Oil & Gas Operator | Jul 2025 |
| 16 | Onyx Properties Corp | Oklahoma City, OK 73114 | Oil & Gas Operator | May 2006 |
| 17 | Opubco Resources Of TX Inc | Dallas, TX 75231 | Oil & Gas Operator | Sep 2005 |
| 18 | Otc Petroleum Corporation | Nichols Hill, OK 73116 | Oil & Gas Operator | Mar 2015 |
| 19 | Overflow Energy, LLC | Perryton, TX 79070 | Oil & Gas Operator | Oct 2025 |
| 20 | Ovintiv Mid-Continent Inc. | The Woodlands, TX 77380-2764 | Oil & Gas Operator | Jun 2025 |
| 21 | Oxy USA Inc | Houston, TX 77046 | Oil & Gas Operator | Oct 2025 |