| 1 | O G & E | Oklahoma City, OK 73124-0300 | Oil & Gas Operator | Feb 2014 |
| 2 | O K Swabbing Inc | Hennessey, OK 73742-0835 | Oil & Gas Operator | Dec 2023 |
| 3 | O'Neill Properties, LTD. | Midland, TX 79702 | Oil & Gas Operator | Apr 2024 |
| 4 | Oak Resources Inc | Tulsa, OK 74153 | Oil & Gas Operator | Aug 2013 |
| 5 | Oil Producers, Inc. Of Kansas | Wichita, KS 67206 | Oil & Gas Operator | Apr 2024 |
| 6 | Oilsearch Corporation | Albuquerque, NM 87109 | Oil & Gas Operator | Feb 1994 |
| 7 | Okie Crude Company | Tulsa, OK 74103 | Oil & Gas Operator | Jan 2024 |
| 8 | Oklahoma Liquid Resources Inc | Owasso, OK 74055-0841 | Oil & Gas Operator | Dec 2023 |
| 9 | Oklahoma Oil & Gas MGMT Inc | | Oil & Gas Operator | Dec 2023 |
| 10 | Oklahoma Petroleum Allies LLC | Ardmore, OK 73401 | Oil Operator | Oct 2023 |
| 11 | Okland Oil Company | Oklahoma City, OK 73102-9022 | Oil & Gas Operator | Jan 2024 |
| 12 | Old Dominion Oil Corporation | Oklahoma City, OK 73107 | Oil & Gas Operator | Apr 2009 |
| 13 | Olympia Oil Inc | Edmond, OK 73083-7088 | Oil & Gas Operator | Jul 2020 |
| 14 | Omimex International Corporation | Fort Worth, TX 76103-2300 | Oil & Gas Operator | Dec 2023 |
| 15 | Oneok Exploration Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 16 | Oneok Resources Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 17 | Onshore Royalties LLC | Houston, TX 77269 | Oil & Gas Operator | Feb 2024 |
| 18 | Onyx Properties Corp | Oklahoma City, OK 73114 | Oil & Gas Operator | May 2006 |
| 19 | Opubco Resources Of TX Inc | Dallas, TX 75231 | Oil & Gas Operator | Sep 2005 |
| 20 | Oryx Crude Trading & Transporation LP | Dallas, TX 75221 | Oil & Gas Operator | Jun 1999 |
| 21 | Otc Petroleum Corporation | Oklahoma City, OK 73116 | Oil & Gas Operator | Mar 2015 |
| 22 | Overflow Energy, LLC | Booker, TX 79005 | Oil & Gas Operator | Apr 2024 |
| 23 | Ovintiv Mid-Continent Inc. | The Woodlands, TX 77380-2764 | Oil & Gas Operator | Jan 2024 |
| 24 | Oxy USA Inc | Houston, TX 77046 | Oil & Gas Operator | Apr 2024 |