| 501 | Optimistic Oil Co. | | Oil & Gas Operator | Dec 1991 |
| 502 | Optimum Exploration LLC | Dallas, TX 75254 | Oil & Gas Operator | Feb 2026 |
| 503 | Opubco Resources Of TX Inc | Dallas, TX 75231 | Oil & Gas Operator | Sep 2005 |
| 504 | Ora Oil Company | | Oil & Gas Operator | May 2017 |
| 505 | Oracle Oil, LLC | | Oil & Gas Operator | Jul 2013 |
| 506 | Oracle Resources Oklahoma LP | Dallas, TX 75240-5751 | Oil & Gas Operator | Feb 2008 |
| 507 | Orange Petroleum Co. | Orangefield, TX 77639 | Oil & Gas Operator | May 1995 |
| 508 | Orangefield Operating Corporation | Dallas, TX 75382 | Oil Operator | Feb 2026 |
| 509 | Orason Resources Inc | Tulsa, OK 74169-1225 | Oil & Gas Operator | Nov 2006 |
| 510 | Orb Exploration, L.L.C. | | Oil & Gas Operator | Jun 2017 |
| 511 | Orbis Energy, L.L.C. | Austin, TX 78746 | Oil & Gas Operator | Oct 2001 |
| 512 | Orbit Crude, Inc. | Midland, TX 79710 | Oil & Gas Operator | Feb 2026 |
| 513 | Orbit Enterprises, Inc. | Lovington, NM 88260 | Oil & Gas Operator | Mar 2015 |
| 514 | Orbit Gas Transmission, Inc | Owensboro, KY 42303 | Oil & Gas Operator | Dec 2023 |
| 515 | Orbit Petroleum, Inc. | Irving, TX 75038 | Oil & Gas Operator | Sep 2010 |
| 516 | Orbitron Operating Corp. | Fort Worth, TX 76102 | Oil & Gas Operator | Dec 1995 |
| 517 | Orbrie Luman | Odessa, TX 79761 | Oil & Gas Operator | Dec 2025 |
| 518 | Orca Operating Company LLC | Houston, TX 77056 | Oil & Gas Operator | Dec 2025 |
| 519 | Oren Stone | Erick, OK 73645-4542 | Gas Operator | Jun 2022 |
| 520 | Oretta Holdings LLC | Houston, TX 77010 | Oil & Gas Operator | Feb 2026 |
| 521 | Orgain, John C. | Graham, TX 76450 | Oil & Gas Operator | Jul 1997 |
| 522 | Organic Energy Company LLC | | Oil & Gas Operator | Jan 2026 |
| 523 | Origin Prod Co Gonzales Prop LLC | New Braunfels, TX 78132 | Oil & Gas Operator | Feb 2026 |
| 524 | Origin Production Company, Inc. | New Braunfels, TX 78132 | Oil & Gas Operator | Feb 2026 |
| 525 | Origin Production Group LLC | Luling, TX 78648 | Oil Operator | Feb 2026 |
| 526 | Oringderff, Alma Oil Properties | Dallas, TX 75225 | Oil & Gas Operator | Mar 2012 |
| 527 | Oriole Operating LLC | Wichita Falls, TX 76308 | Oil Operator | Feb 2026 |
| 528 | Orion Energen Inc. | Austin, TX 78731 | Oil & Gas Operator | Jul 2023 |
| 529 | Orion Energy Corp | MT Vernon, IL 62864 | Oil & Gas Operator | Dec 1984 |
| 530 | Orion Energy Partners LP | Denver, CO 80202 | Oil & Gas Operator | Nov 2010 |
| 531 | Orion Exploration LLC | Tulsa, OK 74105-5153 | Oil & Gas Operator | Apr 2015 |
| 532 | Orion Exploration Partners LLC | Tulsa, OK 74105-5153 | Oil & Gas Operator | Nov 2025 |
| 533 | Orion Oil & Gas Prop | Roswell, NM 88202 | Oil & Gas Operator | Apr 1998 |
| 534 | Orion Oil & Gas Properties | Amarillo, TX 79109 | Gas Operator | Oct 2000 |
| 535 | Orion Oil & Gas, LLC | Houston, TX 77042 | Oil & Gas Operator | Oct 2007 |
| 536 | Orion Oil And Gas Corporation | Houston, TX 77082 | Oil & Gas Operator | Feb 2026 |
| 537 | Orion Petro Corp | MT Vernon, IL 62864 | Oil & Gas Operator | Dec 2016 |
| 538 | Orion Resources, Inc. | San Antonio, TX 78209 | Oil & Gas Operator | Feb 2026 |
| 539 | Orisol Oil Co. | Houston, TX 77206 | Oil Operator | Jun 2000 |
| 540 | Orla Petco Inc & Hopi Drilling Co | Midland, TX 79702 | Oil Operator | Sep 2004 |
| 541 | Orla Petco, Inc. | Midland, TX 79708 | Oil & Gas Operator | Feb 2026 |
| 542 | Orland Oil & Gas LLC | FT Lauderdale, FL 33305 | Oil Operator | Aug 2024 |
| 543 | Orleans Exploration Co., Inc. | | Oil & Gas Operator | Aug 1990 |
| 544 | Orloski John C | Bartlesville, OK 74006 | Oil & Gas Operator | Jun 2025 |
| 545 | Ormand, Don R. | Midland, TX 79705 | Oil & Gas Operator | Jan 2016 |
| 546 | Oro Negro Inc. | | Oil & Gas Operator | Dec 2004 |
| 547 | Oro Resources, LLC | Houston, TX 77024 | Oil & Gas Operator | Feb 2026 |
| 548 | Orphan Wells, LLC | Palmhurst, TX 78573 | Oil & Gas Operator | Feb 2026 |
| 549 | Orr Production Company | Austin, TX 78746 | Oil & Gas Operator | Dec 2000 |
| 550 | Orr Robert W Jr | Zanesville, OH 43702-2683 | Oil & Gas Operator | Dec 2023 |
| 551 | Orr, Jr., Donald R. | Batavia, NY 14020 | Gas Operator | Dec 2024 |
| 552 | Orr, Robert M. | Monahans, TX 79756 | Oil & Gas Operator | Oct 1998 |
| 553 | Orsburn, Wade Inc. | Gainesville, TX 76240 | Oil & Gas Operator | Nov 2002 |
| 554 | Orson Leasing & Supply | Rockdale, TX 76567 | Oil & Gas Operator | Dec 2006 |
| 555 | Orth Oil Company, Inc. | Cisco, TX 76437 | Oil & Gas Operator | Feb 2026 |
| 556 | Orville S Slaughter Jr | Denver, CO 80205 | Oil & Gas Operator | Aug 2000 |
| 557 | Orwig Oil Company Inc | Bradenton, FL 34212 | Oil & Gas Operator | Dec 2022 |
| 558 | Orx Resources, Inc. | | Oil & Gas Operator | Dec 2009 |
| 559 | Orx Resources, L.L.C. | Houston, TX 77067 | Oil & Gas Operator | Feb 2026 |
| 560 | Oryx Energy Comp | | Oil & Gas Operator | Apr 1991 |
| 561 | Oryx Energy Company | Dallas, TX 75221 | Oil & Gas Operator | May 2002 |
| 562 | Os&S Operating Inc. | Electra, TX 76360 | Oil & Gas Operator | Feb 2026 |
| 563 | Osa Oil & Gas LLC | Tulsa, OK 74131 | Oil & Gas Operator | Aug 2023 |
| 564 | Osage Energy Resources LLC | Bartlesville, OK 74005-2527 | Oil & Gas Operator | Nov 2025 |
| 565 | Osage Energy, LLC | Colony, KS 66015 | Oil Operator | Aug 2025 |
| 566 | Osage Exploration & Development Inc | San Diego, CA 92131-3807 | Oil & Gas Operator | Oct 2016 |
| 567 | Osage Hot Oil Service | Newcastle, WY 82701 | Oil & Gas Operator | Jul 1997 |
| 568 | Osage Oil & Transportation Inc | Cleveland, OK 74020 | Oil & Gas Operator | Nov 2000 |
| 569 | Osage Operating Company LLC | Seattle, WA 98133 | Oil Operator | May 2006 |
| 570 | Osage Partners LLC | | Oil & Gas Operator | Jan 2026 |
| 571 | Osage Petroleum Corporation | Saint Louis, MO 63131-4691 | Oil & Gas Operator | Mar 2009 |
| 572 | Osage Resources, LLC | Wichita, KS 67202 | Oil & Gas Operator | May 2025 |
| 573 | Osair Inc | Mentor, OH 44061 | Oil & Gas Operator | Dec 2021 |
| 574 | Osborn Energy, LLC | Bucyrus, KS 66013 | Oil & Gas Operator | Jul 2017 |
| 575 | Osborn Heirs Co | San Antonio, TX 78217 | Oil & Gas Operator | Dec 2025 |
| 576 | Osborn Heirs Com | | Oil & Gas Operator | May 1995 |
| 577 | Osborn Heirs Company LTD | San Antonio, TX 78217 | Oil & Gas Operator | Sep 2025 |
| 578 | Osborn Oil & Gas | | Oil & Gas Operator | Jun 1991 |
| 579 | Osborn,W.B. Oil & Gas Operations | San Antonio, TX 78217 | Oil & Gas Operator | Feb 2026 |
| 580 | Osborne Oil Co. | Dallas, TX 75244 | Oil & Gas Operator | Aug 2003 |
| 581 | Osburn Gerald Dba Ozzy & Son Oil & Gas | Drumright, OK 74030-5467 | Oil Operator | Oct 2020 |
| 582 | Oscar Oil Company | Iowa Park, TX 76367 | Oil & Gas Operator | Sep 2004 |
| 583 | Oscar'S Well Service Inc | Okemah, OK 74859 | Oil & Gas Operator | Apr 1998 |
| 584 | Osceola Oil & Gas Corporation | Somerset, TX 78069 | Oil & Gas Operator | Aug 1994 |
| 585 | Osci Oil And Gas, Inc. | Parker, KS 66072 | Oil Operator | Jun 1998 |
| 586 | Oshtah Oil Company LLC | Stratford, OK 74872 | Oil & Gas Operator | Sep 2018 |
| 587 | Osman Global Services LLC | | Oil & Gas Operator | Jan 2025 |
| 588 | Oso Energy Company | Houston, TX 77280 | Oil & Gas Operator | Feb 1997 |
| 589 | Oso Exploration & Production, LLC | Houston, TX 77269 | Oil Operator | Feb 2026 |
| 590 | Oso Exploration Co. | San Antonio, TX 78217 | Oil & Gas Operator | Jul 2011 |
| 591 | Oso Oil & Gas Properties LLC | Price, UT 84501 | Gas Operator | Jun 2016 |
| 592 | Oso Perdido Services LLC | Flatonia, TX 78941 | Oil Operator | Dec 2025 |
| 593 | Oso Resources LLC | Edmond, OK 73003 | Oil & Gas Operator | Nov 2025 |
| 594 | Ososki Edward D Dba Federal Oil Company | | Oil & Gas Operator | Dec 2025 |
| 595 | Osprey Petroleum Company, Inc. | Manvel, TX 77578 | Oil & Gas Operator | May 2020 |
| 596 | Osr Oil & Gas Company | Victoria, TX 77902 | Oil & Gas Operator | Jul 2000 |
| 597 | Osr Oil & Gas Corp | Midland, TX 79710 | Oil & Gas Operator | Dec 2024 |
| 598 | Osterhout Phillip L | Drumright, OK 74030-0693 | Oil & Gas Operator | Jan 2014 |
| 599 | Ostrich Oil & Gas, LLC | Midland, TX 79701 | Oil & Gas Operator | Feb 2026 |
| 600 | Oswego Arbuckle Enterprise Inc | S Coffeyville, OK 74072-9702 | Oil & Gas Operator | Mar 2015 |