| 1 | O'Boyle Energy Corporation | | Oil Operator | Feb 1991 |
| 2 | O'Brien Energy Company | Shreveport, LA 71136 | Oil & Gas Operator | Sep 2019 |
| 3 | O'Brien Operating Company | Shreveport, LA 71164 | Oil & Gas Operator | Dec 2004 |
| 4 | O'Malley Production Co Inc. | | Oil & Gas Operator | Mar 1988 |
| 5 | O'Meara LLC | | Oil & Gas Operator | Oct 2022 |
| 6 | O'Meara, Inc. | | Oil & Gas Operator | Dec 2006 |
| 7 | O'Sullivan & Scully, Inc. | | Oil & Gas Operator | Oct 1994 |
| 8 | O'Sullivan Oil & Gas Co., Inc. | Houston, TX 77002 | Oil & Gas Operator | Oct 2000 |
| 9 | O. B. And Keith Whatley | | Oil Operator | Jul 1993 |
| 10 | O. B. Beck | | Oil Operator | Feb 1991 |
| 11 | O. B. Mobley | | Oil & Gas Operator | Jul 1989 |
| 12 | O. B. Mobley, Et Al | | Oil Operator | Jul 1989 |
| 13 | O. B. Whatley | | Oil Operator | Jul 1993 |
| 14 | O. D. Maybrier | | Oil Operator | Dec 2011 |
| 15 | O. F. H., Inc. | | Oil Operator | May 1990 |
| 16 | O. G., Inc. | | Oil & Gas Operator | Nov 1992 |
| 17 | O. O. Cummings | | Gas Operator | Jan 1999 |
| 18 | O.B. Whatley Oil Company, Inc. | | Oil Operator | Feb 2013 |
| 19 | O.B., Keith & Owen B. Whatley | | Oil Operator | Jul 1989 |
| 20 | O.G.P. Operating, Inc. | Dallas, TX 75231 | Oil & Gas Operator | Feb 2026 |
| 21 | O.I.L. Energy, Inc. | | Oil & Gas Operator | Dec 1984 |
| 22 | Oak Energy, LLC | Houston, TX 77027 | Oil & Gas Operator | Feb 2026 |
| 23 | Oak Valley Operating, LLC | The Woodlands, TX 77380 | Oil & Gas Operator | Jun 2015 |
| 24 | Oakfield Energy LLC | | Oil Operator | Jun 2019 |
| 25 | Oakland Corporation | | Oil & Gas Operator | Dec 1981 |
| 26 | Oakley Oil & Gas, L.L.C. | | Oil & Gas Operator | Mar 2012 |
| 27 | Oasis Production Co., Inc. | | Oil & Gas Operator | Jun 1988 |
| 28 | Occ Operating Co. | | Oil & Gas Operator | Apr 2019 |
| 29 | Occidental Energy Company, Inc. | Houston, TX 77282 | Oil & Gas Operator | Jul 2021 |
| 30 | Ocean Energy Inc | Houston, TX 77002 | Oil & Gas Operator | Aug 2003 |
| 31 | Octagon Resources Corporation | | Oil Operator | Apr 2005 |
| 32 | Ody Oil Corp. | | Oil & Gas Operator | Oct 1994 |
| 33 | Odyssey Operating Company | Shreveport, LA 71106 | Oil & Gas Operator | Sep 2020 |
| 34 | Offshore Oil & Gas Inc | Houston, TX 77063 | Oil & Gas Operator | Sep 1994 |
| 35 | Offshore Shelf LLC | | Oil & Gas Operator | Dec 2007 |
| 36 | Oil & Gas Development Company | | Oil & Gas Operator | May 1991 |
| 37 | Oil & Gas Producers, Inc | Topeka, KS 66604 | Oil Operator | Jun 2004 |
| 38 | Oil & Gas Property MGMT., Inc. | Dallas, TX 75201 | Oil & Gas Operator | Jul 1996 |
| 39 | Oil And Gas Futures, Inc. | | Oil & Gas Operator | May 1977 |
| 40 | Oil Country Management, Inc. | | Oil & Gas Operator | Jan 2005 |
| 41 | Oil Lift Inc | Metairie, LA 70002 | Oil & Gas Operator | Apr 2020 |
| 42 | Oil Palace, Inc. | | Oil Operator | Jun 2016 |
| 43 | Oil Patch Operators, LLC | | Oil & Gas Operator | Jul 2005 |
| 44 | Oil Recovery, Inc. | | Oil Operator | Sep 1992 |
| 45 | Oil Reserves Corp Of America | | Oil & Gas Operator | May 2002 |
| 46 | Oil Well Buyers Corp. | Houston, TX 77056 | Oil & Gas Operator | Dec 2024 |
| 47 | Oil,Gas & Other Minerals, Inc. | | Oil & Gas Operator | Apr 1996 |
| 48 | Oilfield Technical Services, Inc. | | Gas Operator | Jun 2018 |
| 49 | Oilwell Acquisition Co | | Oil & Gas Operator | Jun 1999 |
| 50 | Ok Oil Company, Inc. | Bivins, TX 75555 | Oil & Gas Operator | Feb 2013 |
| 51 | Ok-La-Tex Production, Inc. | | Oil & Gas Operator | Jan 1982 |
| 52 | Okie Crude Company | Tulsa, OK 74103 | Oil & Gas Operator | Nov 2025 |
| 53 | Okie Operating Company, LTD. | Tulsa, OK 74103 | Oil & Gas Operator | Feb 2026 |
| 54 | Okkatahula, Inc. | | Oil Operator | Nov 1978 |
| 55 | Oldfield Operating Corporation | | Oil Operator | Dec 2013 |
| 56 | Oleum Inc | | Oil & Gas Operator | Mar 1996 |
| 57 | Oleum Operating Company, L.C. | Longview, TX 75606 | Oil & Gas Operator | Dec 2021 |
| 58 | Oleum Operating La LLC | | Oil & Gas Operator | Nov 2022 |
| 59 | Oliditt Corporation | | Gas Operator | Mar 2022 |
| 60 | Oliditt Production Inc. | | Gas Operator | Sep 1998 |
| 61 | Olipdp II, LLC | Lafayette, LA 70503 | Oil & Gas Operator | Feb 2026 |
| 62 | Olympic Natural Gas Company | | Oil & Gas Operator | Oct 1990 |
| 63 | Olympic Oil & Gas Co., Inc. | | Oil Operator | Apr 1991 |
| 64 | Olympic Oil & Gas Expl. Co. | | Oil & Gas Operator | Nov 1987 |
| 65 | Olympic Petroleum Co | Tulsa, OK 74114 | Oil & Gas Operator | Jun 1998 |
| 66 | Olympic Production Company | | Oil & Gas Operator | Jul 1994 |
| 67 | Omeara Bros. | | Oil & Gas Operator | Oct 1982 |
| 68 | Omega Energy Corp. | Graham, TX 76450 | Oil & Gas Operator | Feb 2026 |
| 69 | Omega Energy Incorporated | | Oil & Gas Operator | May 1998 |
| 70 | Omni Operating Company | Osage, WY 82723 | Oil & Gas Operator | Sep 2001 |
| 71 | Onshore Exp Cor-La Nat Res Inc | | Oil & Gas Operator | Oct 1978 |
| 72 | Onshore Pipeline Const Co Inc | | Oil & Gas Operator | Aug 1998 |
| 73 | Onyx Energy Corporation | Oklahoma City, OK 73157 | Oil & Gas Operator | May 1994 |
| 74 | Onyx Energy Dev Of Texas Inc. | | Oil Operator | Dec 1996 |
| 75 | Onyx Energy Of Texas Inc. | | Oil Operator | Dec 1996 |
| 76 | Onyxx Energy LLC | | Oil & Gas Operator | Mar 2017 |
| 77 | Opal Oil Inc. | | Oil Operator | Sep 2021 |
| 78 | Opmi Operating Company | Houston, TX 77057 | Oil & Gas Operator | Jun 2008 |
| 79 | Ops Group Limited | Houston, TX 77060 | Oil & Gas Operator | Jun 2014 |
| 80 | Optimistic Oil Co. | | Oil & Gas Operator | Dec 1991 |
| 81 | Ora Oil Company | | Oil & Gas Operator | May 2017 |
| 82 | Oracle Oil, LLC | | Oil & Gas Operator | Jul 2013 |
| 83 | Orb Exploration, L.L.C. | | Oil & Gas Operator | Jun 2017 |
| 84 | Orion Oil & Gas, LLC | Houston, TX 77042 | Oil & Gas Operator | Oct 2007 |
| 85 | Orleans Exploration Co., Inc. | | Oil & Gas Operator | Aug 1990 |
| 86 | Orx Resources, Inc. | | Oil & Gas Operator | Dec 2009 |
| 87 | Orx Resources, L.L.C. | Houston, TX 77067 | Oil & Gas Operator | Feb 2026 |
| 88 | Oryx Energy Company | Dallas, TX 75221 | Oil & Gas Operator | May 2002 |
| 89 | Osman Global Services LLC | | Oil & Gas Operator | Jan 2025 |
| 90 | Osr Oil & Gas Corp | Midland, TX 79710 | Oil & Gas Operator | Dec 2024 |
| 91 | Osyka Permian, LLC | Houston, TX 77079 | Oil & Gas Operator | Feb 2026 |
| 92 | Otis C. Coles, Jr. | | Oil & Gas Operator | Jan 1998 |
| 93 | Ouachita Development Corp. | | Gas Operator | Mar 2014 |
| 94 | Ouida Oil Co. | | Oil & Gas Operator | Apr 1999 |
| 95 | Output Acquisition Corp. | | Oil & Gas Operator | Jul 2010 |
| 96 | Owen Production Co | | Oil Operator | May 2001 |
| 97 | Owl Creek Production Co., Inc. | Houston, TX 77027 | Oil & Gas Operator | Apr 2006 |
| 98 | Oxbow EP LLC | Mathis, TX 78368 | Oil Operator | Feb 2026 |
| 99 | Oxford Exploration Company | Denver, CO 80237 | Oil & Gas Operator | Aug 1995 |
| 100 | Oxtex Inc | | Oil & Gas Operator | Oct 1989 |