| 20501 | Occidental Petroleum Corporation | | Oil & Gas Operator | Dec 2021 |
| 20502 | Occidental W TX Overthrust, Inc. | Houston, TX 77210 | Oil & Gas Operator | Dec 2021 |
| 20503 | Ocean Energy Inc | Houston, TX 77002 | Oil & Gas Operator | Aug 2003 |
| 20504 | Ocean Energy Resources Inc. | Houston, TX 77002 | Oil & Gas Operator | Mar 2025 |
| 20505 | Ocfiw Oil Company, Inc. | Hartington, NE 68739 | Oil & Gas Operator | Dec 2009 |
| 20506 | Ochiltree Oil Company | Edmond, OK 73034 | Oil & Gas Operator | Apr 2020 |
| 20507 | Oci LLC | Thermopolis, WY 82443 | Oil Operator | Jan 2024 |
| 20508 | Ocotillo Energy Resources, LLC | Odessa, TX 79765 | Oil Operator | Apr 2026 |
| 20509 | Octagon Resources Corporation | | Oil Operator | Apr 2005 |
| 20510 | Octagon Resources LLC | Norman, OK 73071-1295 | Oil & Gas Operator | May 2015 |
| 20511 | Octane Energy Operating, LLC | Midland, TX 79701 | Oil & Gas Operator | Apr 2026 |
| 20512 | Odebralski, Michael & Connie | Fredonia, NY 14063 | Gas Operator | Dec 2024 |
| 20513 | Odegard Energy, Inc. | Houston, TX 77024 | Oil & Gas Operator | Jul 2020 |
| 20514 | Odegard Resources/Omni Exp | Columbus, OH 43207 | Oil & Gas Operator | Sep 1986 |
| 20515 | Odell Larry | Oologah, OK 74053 | Oil Operator | Apr 2011 |
| 20516 | Oden, Robin H., Inc. | Midland, TX 79702 | Oil & Gas Operator | Apr 1994 |
| 20517 | Odessa Exploration, Inc. | Midland, TX 79702 | Oil & Gas Operator | Apr 2026 |
| 20518 | Odessa Oil Investment Co., Inc. | Odessa, TX 79762 | Oil & Gas Operator | Nov 2016 |
| 20519 | Odom, Claude | | Oil Operator | Jul 1983 |
| 20520 | Odom, R. H. | Snyder, TX 79550 | Oil & Gas Operator | Jun 1996 |
| 20521 | Odom, Ralph R. | | Oil & Gas Operator | Aug 1993 |
| 20522 | Odum Oil & Gas Co. | Harper, TX 78631 | Oil & Gas Operator | Apr 2026 |
| 20523 | Odum Ronald L | Ponca City, OK 74601 | Oil Operator | Jan 2026 |
| 20524 | Ody Oil Corp. | | Oil & Gas Operator | Oct 1994 |
| 20525 | Odyssey Operating Company | Shreveport, LA 71106 | Oil & Gas Operator | Sep 2020 |
| 20526 | Odyssey Petroleum Company | Houston, TX 77010 | Oil & Gas Operator | Apr 1995 |
| 20527 | Odyssey Petroleum Corp. | | Oil & Gas Operator | Jun 2011 |
| 20528 | Oedekoven Amerifields Resources LLC | Sugar Land, TX 77478 | Oil Operator | Dec 2025 |
| 20529 | Oedekoven Water & Hot Oil | Recluse, WY 82725 | Oil & Gas Operator | Feb 2026 |
| 20530 | Oeth DRLG Co | | Oil Operator | Dec 2018 |
| 20531 | Oex-1 LLC | Tulsa, OK 74105-5153 | Oil & Gas Operator | Mar 2024 |
| 20532 | Oexco, Inc. | Tulsa, OK 74136 | Oil & Gas Operator | Mar 2015 |
| 20533 | Off Broadway Mineral Rights LLC | | Oil & Gas Operator | Oct 2024 |
| 20534 | Offield Lease Operations LLC | Wilson, OK 73463 | Oil & Gas Operator | May 2023 |
| 20535 | Offset Oil & Gas | Big Spring, TX 79720 | Oil & Gas Operator | Aug 2003 |
| 20536 | Offshore Group, Inc. The | Houston, TX 77024 | Oil & Gas Operator | Apr 2026 |
| 20537 | Offshore Oil & Gas Inc | Houston, TX 77063 | Oil & Gas Operator | Sep 1994 |
| 20538 | Offshore Shelf LLC | | Oil & Gas Operator | Dec 2007 |
| 20539 | Ofs-Tulsa Corporation | Fort Worth, TX 76102 | Oil & Gas Operator | Feb 1997 |
| 20540 | Oft Inc. | Houston, TX 77079 | Oil & Gas Operator | Apr 2026 |
| 20541 | Og Co., Inc. | Houston, TX 77057 | Oil & Gas Operator | Apr 2026 |
| 20542 | Oga Operating L.L.C. | Midland, TX 79702 | Oil & Gas Operator | Jan 2000 |
| 20543 | Ogden Oil Co., Inc. | | Oil Operator | May 1981 |
| 20544 | Ogden Resources Corporation | Bryan, TX 77805 | Oil & Gas Operator | Apr 2026 |
| 20545 | Ogden Resources, LTD. | Bryan, TX 77802 | Oil & Gas Operator | Feb 2009 |
| 20546 | Ogh Oil Company | | Oil Operator | Sep 1995 |
| 20547 | Ogle Petroleum Inc. | | Oil & Gas Operator | Dec 1989 |
| 20548 | Oglesby Oil Company | | Oil & Gas Operator | Nov 2023 |
| 20549 | Oglesby Prod & Expl Co Inc | | Oil & Gas Operator | Nov 1987 |
| 20550 | Oglesby, Marshall | | Oil Operator | May 1990 |
| 20551 | Ogog Operating, LLC | Dallas, TX 75367 | Oil & Gas Operator | Apr 2026 |
| 20552 | Ogris Operating, LLC | Midland, TX 79710 | Oil & Gas Operator | Apr 2026 |
| 20553 | Ogs Operating Company, Inc. | Midland, TX 79701 | Oil & Gas Operator | Sep 2008 |
| 20554 | Ogx Operating, LLC | Midland, TX 79702 | Oil & Gas Operator | Apr 2026 |
| 20555 | Ogx Resources LLC | Midland, TX 79702 | Oil & Gas Operator | Oct 2011 |
| 20556 | Ohio Energy Assets, Inc. | Laurelville, OH 43135 | Oil & Gas Operator | Dec 2014 |
| 20557 | Ohio Energy Group Inc | Uniontown, OH 44685 | Oil & Gas Operator | Dec 1988 |
| 20558 | Ohio Energy Operators LLC | Colorado Spring, CO 80908 | Oil Operator | Dec 2018 |
| 20559 | Ohio Kentucky Oil Corporation | Lexington, KY 40503 | Oil & Gas Operator | Dec 2024 |
| 20560 | Ohio L & M Company Inc | Marietta, OH 45750 | Oil & Gas Operator | Dec 2008 |
| 20561 | Ohio Natural Fuel Co | Canton, OH 44718 | Oil & Gas Operator | Dec 1985 |
| 20562 | Ohio Oil & Gas | Fowler, OH 44418 | Oil & Gas Operator | Dec 1988 |
| 20563 | Ohio Production Corp | Westerville, OH 43081 | Oil & Gas Operator | Dec 2001 |
| 20564 | Ohio Production* | Newark, OH 43055 | Oil & Gas Operator | Dec 1987 |
| 20565 | Ohio Valley Energy Systems Corp | Austintown, OH 44515 | Oil & Gas Operator | Dec 2025 |
| 20566 | Ohio Valley Energy, Inc | Livermore, KY 42352 | Oil Operator | Dec 2023 |
| 20567 | Ohlhausen Oil Company | Abilene, TX 79608 | Oil & Gas Operator | Apr 2026 |
| 20568 | Oi Auburn, Inc. | Tulsa, OK 74135 | Gas Operator | Dec 2024 |
| 20569 | Oil & Gas Acquisition Group Inc | Austin, TX 78716 | Oil & Gas Operator | May 2003 |
| 20570 | Oil & Gas Development Company | | Oil & Gas Operator | May 1991 |
| 20571 | Oil & Gas Exploration Inc | Cleveland, OK 74020 | Oil & Gas Operator | Aug 2013 |
| 20572 | Oil & Gas MGMT Inc | Mount Pleasant, PA 15666-3304 | Oil & Gas Operator | Dec 2024 |
| 20573 | Oil & Gas Operations | Midland, TX 79706 | Oil & Gas Operator | Apr 2026 |
| 20574 | Oil & Gas Producers, Inc | Topeka, KS 66604 | Oil Operator | Jun 2004 |
| 20575 | Oil & Gas Properties | Midland, TX 79704 | Oil & Gas Operator | Apr 2026 |
| 20576 | Oil & Gas Property MGMT., Inc. | Dallas, TX 75201 | Oil & Gas Operator | Jul 1996 |
| 20577 | Oil & Gas Servic | | Oil Operator | Jun 1983 |
| 20578 | Oil & Gas Solutions LTD | Wooster, OH 44691 | Oil & Gas Operator | Dec 2007 |
| 20579 | Oil & Gas SVC Inc | Reelsville, IN 46171-9686 | Gas Operator | Dec 1991 |
| 20580 | Oil & Realty Devlop Inc | Columbus, OH 43212 | Oil Operator | Dec 1986 |
| 20581 | Oil And Gas Futures, Inc. | | Oil & Gas Operator | May 1977 |
| 20582 | Oil And Gas Management, Inc. | Kansas City, MO 64106 | Oil Operator | Apr 2011 |
| 20583 | Oil Capital Corporation | Littleton, CO 80122 | Gas Operator | May 2009 |
| 20584 | Oil Capital Operating, LLC | Tulsa, OK 74103 | Oil & Gas Operator | Apr 2026 |
| 20585 | Oil Center Operating Inc | Fort Worth, TX 76102-5108 | Oil & Gas Operator | Apr 2014 |
| 20586 | Oil Coast Corp. | S Houston, TX 77587 | Oil & Gas Operator | Apr 2026 |
| 20587 | Oil Company Of America, Inc. | Hays, KS 67601 | Oil Operator | Dec 2009 |
| 20588 | Oil Country Management, Inc. | | Oil & Gas Operator | Jan 2005 |
| 20589 | Oil Creek Operators LLC | Franklin, PA 16323 | Oil Operator | Dec 2025 |
| 20590 | Oil Creek Production Company | Prague, OK 74864-0667 | Oil & Gas Operator | Dec 2025 |
| 20591 | Oil Development Co | | Oil & Gas Operator | Jan 1979 |
| 20592 | Oil Drillers & D | | Oil & Gas Operator | Feb 1992 |
| 20593 | Oil Enterprises | Logan, OH 43138 | Oil & Gas Operator | Dec 2025 |
| 20594 | Oil Exploration Of America Inc | Sisseton, SD 57262-9503 | Oil & Gas Operator | Jun 2001 |
| 20595 | Oil Field Manage | | Oil Operator | Jun 1991 |
| 20596 | Oil Inc | | Oil & Gas Operator | Dec 1971 |
| 20597 | Oil Internationa | | Oil Operator | Jun 1986 |
| 20598 | Oil Investors Inc | Crescent, OK 73028 | Oil & Gas Operator | Feb 2026 |
| 20599 | Oil Lease Operating Co. | Coldspring, TX 77331 | Oil & Gas Operator | Aug 2003 |
| 20600 | Oil Lift Inc | Metairie, LA 70002 | Oil & Gas Operator | Apr 2020 |