| 21001 | Oakland Corporation | | Oil & Gas Operator | Dec 1981 |
| 21002 | Oakland Petroleum Oper Co., Inc. | Kilgore, TX 75663 | Oil & Gas Operator | May 2025 |
| 21003 | Oakley Oil & Gas, L.L.C. | | Oil & Gas Operator | Mar 2012 |
| 21004 | Oakmont CC | Oakmont, PA 15139-1135 | Gas Operator | Dec 2024 |
| 21005 | Oakmont Oil And Gas | Graham, TX 76450 | Oil Operator | May 2025 |
| 21006 | Oakridge Energy, Inc. | Wichita Falls, TX 76302 | Oil & Gas Operator | May 2025 |
| 21007 | Oakridge Oil And Gas, LP | Jacksboro, TX 76458 | Oil & Gas Operator | May 2025 |
| 21008 | Oaks Petroleum I | | Oil Operator | Jul 1987 |
| 21009 | Oaktree Oil Company | Albany, TX 76430 | Oil & Gas Operator | May 2025 |
| 21010 | Oakwood Energy, Inc. | Jourdanton, TX 78026 | Oil & Gas Operator | Mar 2023 |
| 21011 | Oakwood Resources, Inc. | Dallas, TX 75374 | Oil & Gas Operator | May 1998 |
| 21012 | Oasis Energy Resources LLC | Norman, OK 73072-9668 | Oil & Gas Operator | Feb 2025 |
| 21013 | Oasis Operating, Inc. | Lubbock, TX 79404 | Oil & Gas Operator | Nov 2020 |
| 21014 | Oasis Petroleum | | Gas Operator | Feb 1984 |
| 21015 | Oasis Petroleum North America LLC | Houston, TX 77002 | Oil & Gas Operator | Mar 2025 |
| 21016 | Oasis Petroleum Permian LLC | Houston, TX 77002 | Oil & Gas Operator | May 2025 |
| 21017 | Oasis Production Co., Inc. | | Oil & Gas Operator | Jun 1988 |
| 21018 | Oast, Thomas H. | Greenville, NC 27835 | Oil Operator | Nov 1985 |
| 21019 | Oates, John Co., Inc. | Stinnett, TX 79083 | Oil & Gas Operator | May 2025 |
| 21020 | Obax Oil And Gas LLC | Saint Louis, MO 63131 | Oil Operator | May 2025 |
| 21021 | Obele Oil Corporation | Sedona, AZ 86336-5745 | Oil & Gas Operator | May 2017 |
| 21022 | Obele Operating Company LLC | Sedona, AZ 86336-5745 | Oil & Gas Operator | Feb 2025 |
| 21023 | Oberlander Leslie A Jake | Covington, OK 73730 | Oil Operator | Jun 2007 |
| 21024 | Obermiller Clarence Trust | Creston, OH 44217 | Oil & Gas Operator | Dec 1987 |
| 21025 | Obermiller Paul J | Creston, OH 44217 | Oil & Gas Operator | Dec 2014 |
| 21026 | Oblaen Resources LLC | Wallis, TX 77485 | Oil & Gas Operator | May 2025 |
| 21027 | Occ Operating Co. | | Oil & Gas Operator | Apr 2019 |
| 21028 | Occidental Energy Company, Inc. | Houston, TX 77282 | Oil & Gas Operator | Jul 2021 |
| 21029 | Occidental Energy Marketing, Inc. | Houston, TX 77227 | Gas Operator | Sep 2015 |
| 21030 | Occidental Of Elk Hills Inc. | | Oil & Gas Operator | Dec 2014 |
| 21031 | Occidental Permian LTD. | Houston, TX 77046 | Oil & Gas Operator | May 2025 |
| 21032 | Occidental Petroleum Corporation | | Oil & Gas Operator | Dec 2021 |
| 21033 | Occidental W TX Overthrust, Inc. | Houston, TX 77210 | Oil & Gas Operator | Dec 2021 |
| 21034 | Ocean Energy Inc Ndba Devon Louisiana Corp | | Oil & Gas Operator | Jul 2001 |
| 21035 | Ocean Energy Resources Inc. | Houston, TX 77002 | Oil & Gas Operator | Jan 2025 |
| 21036 | Ocean Energy, Inc. | Houston, TX 77002 | Oil & Gas Operator | Aug 2003 |
| 21037 | Ocfiw Oil Company, Inc. | Hartington, NE 68739 | Oil & Gas Operator | Dec 2009 |
| 21038 | Ochiltree Oil Company | Edmond, OK 73034 | Oil & Gas Operator | Apr 2020 |
| 21039 | Oci LLC | Thermopolis, WY 82443 | Oil Operator | Jan 2024 |
| 21040 | Octagon Resources Corporation | | Oil Operator | Apr 2005 |
| 21041 | Octagon Resources LLC | Norman, OK 73071-1295 | Oil & Gas Operator | May 2015 |
| 21042 | Octane Energy Operating, LLC | Midland, TX 79701 | Oil & Gas Operator | May 2025 |
| 21043 | Odebralski, Michael & Connie | Fredonia, NY 14063 | Gas Operator | Dec 2023 |
| 21044 | Odegard Energy, Inc. | Houston, TX 77024 | Oil & Gas Operator | Jul 2020 |
| 21045 | Odegard Resources/Omni Exp | Columbus, OH 43207 | Oil & Gas Operator | Sep 1986 |
| 21046 | Odell Larry | Oologah, OK 74053 | Oil Operator | Apr 2011 |
| 21047 | Oden, Robin H., Inc. | Midland, TX 79702 | Oil & Gas Operator | Apr 1994 |
| 21048 | Odessa Exploration, Inc. | Midland, TX 79702 | Oil & Gas Operator | May 2025 |
| 21049 | Odessa Oil Investment Co., Inc. | Odessa, TX 79762 | Oil & Gas Operator | Nov 2016 |
| 21050 | Odom, Claude | | Oil Operator | Jul 1983 |
| 21051 | Odom, R. H. | Snyder, TX 79550 | Oil & Gas Operator | Jun 1996 |
| 21052 | Odom, Ralph R. | | Oil & Gas Operator | Aug 1993 |
| 21053 | Odum Oil & Gas Co. | Harper, TX 78631 | Oil & Gas Operator | May 2025 |
| 21054 | Odum Ronald L | Garfield, AR 72732 | Oil Operator | Feb 2025 |
| 21055 | Ody Oil Corp. | | Oil & Gas Operator | Oct 1994 |
| 21056 | Odyssey Operating Company | | Oil & Gas Operator | Sep 2020 |
| 21057 | Odyssey Petroleum Company | Houston, TX 77010 | Oil & Gas Operator | Apr 1995 |
| 21058 | Odyssey Petroleum Corp. | | Oil & Gas Operator | Jun 2011 |
| 21059 | Odyssey Petroleum, Inc. | Overland Park, KS 66282 | Oil & Gas Operator | Apr 2009 |
| 21060 | Oedekoven Amerifields Resources LLC | Sugar Land, TX 77478 | Oil Operator | Feb 2025 |
| 21061 | Oedekoven Water & Hot Oil | Recluse, WY 82725 | Oil & Gas Operator | Apr 2025 |
| 21062 | Oeth DRLG Co | | Oil Operator | Dec 2018 |
| 21063 | Oex-1 LLC | Tulsa, OK 74105-5153 | Oil & Gas Operator | Mar 2024 |
| 21064 | Oexco, Inc. | Tulsa, OK 74136 | Oil & Gas Operator | Mar 2015 |
| 21065 | Off Broadway Mineral Rights LLC | | Oil & Gas Operator | Oct 2024 |
| 21066 | Offield Lease Operations LLC | Wilson, OK 73463 | Oil & Gas Operator | May 2023 |
| 21067 | Offset Oil & Gas | Big Spring, TX 79720 | Oil & Gas Operator | Aug 2003 |
| 21068 | Offshore Group, Inc. The | Houston, TX 77024 | Oil & Gas Operator | May 2025 |
| 21069 | Offshore Oil & Gas Inc | Houston, TX 77063 | Oil & Gas Operator | Sep 1994 |
| 21070 | Offshore Shelf LLC | | Oil & Gas Operator | Dec 2007 |
| 21071 | Ofs-Tulsa Corporation | Fort Worth, TX 76102 | Oil & Gas Operator | Feb 1997 |
| 21072 | Oft Inc. | Houston, TX 77079 | Oil & Gas Operator | May 2025 |
| 21073 | Og Co., Inc. | Houston, TX 77057 | Oil & Gas Operator | May 2025 |
| 21074 | Oga Operating L.L.C. | Midland, TX 79702 | Oil & Gas Operator | Jan 2000 |
| 21075 | Ogden Oil Co., Inc. | | Oil Operator | May 1981 |
| 21076 | Ogden Resources Corporation | Bryan, TX 77802 | Oil & Gas Operator | May 2025 |
| 21077 | Ogden Resources, LTD. | Bryan, TX 77802 | Oil & Gas Operator | Feb 2009 |
| 21078 | Ogh Oil Company | | Oil Operator | Sep 1995 |
| 21079 | Ogle Petroleum Inc. | | Oil & Gas Operator | Dec 1989 |
| 21080 | Oglesby Oil Company | | Oil & Gas Operator | Nov 2023 |
| 21081 | Oglesby Prod & Expl Co Inc | | Oil & Gas Operator | Nov 1987 |
| 21082 | Oglesby, Marshall | | Oil Operator | May 1990 |
| 21083 | Ogog Operating, LLC | Dallas, TX 75367 | Oil & Gas Operator | May 2025 |
| 21084 | Ogris Operating LLC | | Gas Operator | Mar 2025 |
| 21085 | Ogs Operating Company, Inc. | Midland, TX 79701 | Oil & Gas Operator | Sep 2008 |
| 21086 | Ogx Operating, LLC | Midland, TX 79702 | Oil & Gas Operator | May 2025 |
| 21087 | Ogx Resources LLC | Midland, TX 79702 | Oil & Gas Operator | Oct 2011 |
| 21088 | Ohio Energy Assets, Inc. | Laurelville, OH 43135 | Oil & Gas Operator | Dec 2014 |
| 21089 | Ohio Energy Group Inc | Uniontown, OH 44685 | Oil & Gas Operator | Dec 1988 |
| 21090 | Ohio Energy Operators LLC | Colorado Spring, CO 80908 | Oil Operator | Dec 2018 |
| 21091 | Ohio Investment Leas Inc | Danville, OH 43014 | Oil & Gas Operator | Dec 1989 |
| 21092 | Ohio Kentucky Oil Corporation | Lexington, KY 40503 | Oil & Gas Operator | Dec 2023 |
| 21093 | Ohio L & M Company Inc | Marietta, OH 45750 | Oil & Gas Operator | Dec 2008 |
| 21094 | Ohio Natural Fuel Co | Canton, OH 44718 | Oil & Gas Operator | Dec 1985 |
| 21095 | Ohio Oil & Gas | Fowler, OH 44418 | Oil & Gas Operator | Dec 1988 |
| 21096 | Ohio Production Corp | Westerville, OH 43081 | Oil & Gas Operator | Dec 2001 |
| 21097 | Ohio Production* | Newark, OH 43055 | Oil & Gas Operator | Dec 1987 |
| 21098 | Ohio Valley Energy Systems Corp | Austintown, OH 44515 | Oil & Gas Operator | Dec 2024 |
| 21099 | Ohio Valley Energy, Inc | Livermore, KY 42352 | Oil Operator | Dec 2023 |
| 21100 | Ohlhausen Oil Company | Abilene, TX 79608 | Oil & Gas Operator | May 2025 |