| 21301 | Olson D Producti | | Oil Operator | Jul 1994 |
| 21302 | Olson, S. A. | Kenedy, TX 78119 | Oil & Gas Operator | Aug 1994 |
| 21303 | Olson-Anderson Lease | | Oil Operator | Mar 2018 |
| 21304 | Oltex Production | Idalou, TX 79329 | Oil & Gas Operator | May 2025 |
| 21305 | Olympia Oil Inc | Edmond, OK 73083-7088 | Oil & Gas Operator | Jul 2020 |
| 21306 | Olympic Exploration & Production Co | Norman, OK 73072 | Oil Operator | May 2003 |
| 21307 | Olympic Exploration Inc | Denver, CO 80202 | Oil & Gas Operator | Jul 2004 |
| 21308 | Olympic Natural Gas Company | | Oil & Gas Operator | Oct 1990 |
| 21309 | Olympic Oil & Gas Co., Inc. | | Oil Operator | Apr 1991 |
| 21310 | Olympic Oil, Inc. | Hutchinson, KS 67502 | Oil & Gas Operator | Dec 2024 |
| 21311 | Olympic Petroleu | | Oil & Gas Operator | Jul 1993 |
| 21312 | Olympic Petroleum Company | Tulsa, OK 74114 | Oil & Gas Operator | Jun 1998 |
| 21313 | Olympic Production Company | | Oil & Gas Operator | Jul 1994 |
| 21314 | Olympic Resources Co | Wooster, OH 44691 | Oil & Gas Operator | Dec 2000 |
| 21315 | Olympus Energy, LLC | Canonsburg, PA 15317 | Gas Operator | Mar 2025 |
| 21316 | Olympus Prop Inc | Franklin Park, IL 60131-1418 | Oil & Gas Operator | Dec 1997 |
| 21317 | Omac Oil & Gas Co | Newark, OH 43055 | Oil & Gas Operator | Dec 1990 |
| 21318 | Omar Operating Company | Midland, TX 79702 | Oil & Gas Operator | Sep 2013 |
| 21319 | Omber Petroleum & Energy Corp. | New Braunfels, TX 78131 | Oil & Gas Operator | May 2025 |
| 21320 | Omeara Bros. | | Oil & Gas Operator | Oct 1982 |
| 21321 | Omega Alpha Resources, LLC | Dallas, TX 75219 | Oil Operator | May 2025 |
| 21322 | Omega Energy Corp. | Graham, TX 76450 | Oil & Gas Operator | May 2025 |
| 21323 | Omega Energy Incorporated | | Oil & Gas Operator | May 1998 |
| 21324 | Omega Energy, LLC | Corpus Chrsti, TX 78418 | Oil & Gas Operator | May 2025 |
| 21325 | Omega Enterprise | | Oil Operator | Sep 1990 |
| 21326 | Omega Oil Corp | Lafayette, IN 47903 | Oil & Gas Operator | Dec 1987 |
| 21327 | Omega Operating, Inc. | Odessa, TX 79769 | Oil & Gas Operator | Mar 2001 |
| 21328 | Omega Resources Inc | | Oil & Gas Operator | Nov 1998 |
| 21329 | Omimex Canada, LTD. | Fort Worth, TX 76120-3608 | Oil & Gas Operator | Mar 2025 |
| 21330 | Omimex Energy, Inc. | Fort Worth, TX 76120 | Oil & Gas Operator | Jan 2025 |
| 21331 | Omimex International Corp | Fort Worth, TX 76103-2300 | Oil & Gas Operator | Feb 2025 |
| 21332 | Omimex Petroleum Inc | Fort Worth, TX 76120 | Oil & Gas Operator | Aug 2022 |
| 21333 | Omimex Petroleum Inc (Co) | Newcastle, WY 82701 | Oil & Gas Operator | May 2001 |
| 21334 | Omimex Petroleum Inc (De) | Fort Worth, TX 76120 | Oil & Gas Operator | Aug 2020 |
| 21335 | Omni E & P, Inc. | San Antonio, TX 78229 | Oil Operator | Apr 2010 |
| 21336 | Omni Oil & Gas, Inc. | San Antonio, TX 78229 | Oil & Gas Operator | Oct 2017 |
| 21337 | Omni Operating Company | Osage, WY 82723 | Oil & Gas Operator | Sep 2001 |
| 21338 | Omni Operating Company(A) | Dallas, TX 75370 | Oil & Gas Operator | May 2025 |
| 21339 | Omni Petroleum Corporation | Austin, TX 78738 | Oil & Gas Operator | May 2025 |
| 21340 | Omr Drilling & Acquisition LLC | Albany, KY 42602 | Oil Operator | Dec 2015 |
| 21341 | On Pointe Operating LLC | Jones, OK 73049 | Oil & Gas Operator | May 2025 |
| 21342 | On-Line Oil Inc | Oklahoma City, OK 73105-5208 | Oil & Gas Operator | Mar 2015 |
| 21343 | Onapa Gas Company LLC | Tulsa, OK 74136-7253 | Gas Operator | Nov 2019 |
| 21344 | Onaroll Operating LLC | Levelland, TX 79336 | Oil Operator | May 2025 |
| 21345 | Onco Petroleum USA Inc | | Oil Operator | Dec 2009 |
| 21346 | One Epoch Energy, Inc. | Abilene, TX 79604 | Oil & Gas Operator | Mar 2008 |
| 21347 | One Nickel Operating LLC | Westbrook, TX 79565 | Oil Operator | May 2025 |
| 21348 | One Source Financial Services Inc. | McAllen, TX 78501 | Gas Operator | Dec 2019 |
| 21349 | One Tec Operating, LLC | Houston, TX 77002 | Oil & Gas Operator | Nov 2007 |
| 21350 | One World Operating, LLC | Tampa, FL 33602 | Oil & Gas Operator | May 2025 |
| 21351 | Oneenergy Partners Operating, LLC | Houston, TX 77019 | Oil & Gas Operator | Nov 2018 |
| 21352 | Oneida Energy Corporation | Tulsa, OK 74137 | Oil & Gas Operator | Jul 2003 |
| 21353 | Oneok Bushton Proces | | Gas Operator | Mar 2007 |
| 21354 | Oneok Energy Service | | Gas Operator | Dec 2008 |
| 21355 | Oneok Exploratio | | Oil & Gas Operator | Mar 1995 |
| 21356 | Oneok Exploration Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 21357 | Oneok Field Services Company | Tulsa, OK 74103 | Oil & Gas Operator | Jul 2022 |
| 21358 | Oneok Gas Processing LLC | Tulsa, OK 74103 | Oil & Gas Operator | May 2018 |
| 21359 | Oneok Gas Transportation Co | Tulsa, OK 74121-2089 | Oil & Gas Operator | Oct 2014 |
| 21360 | Oneok Resources Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 21361 | Onexxx Prod & Exploration Corp | Jeannette, PA 15644-9691 | Gas Operator | Dec 2024 |
| 21362 | Onnen, Gerhard E. | Yates Center, KS 66783 | Oil Operator | Feb 2002 |
| 21363 | Onpoint Oil & Gas LLC | Oklahoma City, OK 73170-4848 | Oil & Gas Operator | Feb 2025 |
| 21364 | Onshore Exp Cor-La Nat Res Inc | | Oil & Gas Operator | Oct 1978 |
| 21365 | Onshore Pipeline Const Co Inc | | Oil & Gas Operator | Aug 1998 |
| 21366 | Onshore Royalties LLC | Houston, TX 77269 | Oil & Gas Operator | Mar 2025 |
| 21367 | Onshore, L.L.C. | Wichita, KS 67205 | Oil & Gas Operator | Dec 2009 |
| 21368 | Onyx Energy Corporation | Oklahoma City, OK 73157 | Oil & Gas Operator | May 1994 |
| 21369 | Onyx Energy Dev Of Texas Inc. | | Oil Operator | Dec 1996 |
| 21370 | Onyx Energy Of Texas Inc. | | Oil Operator | Dec 1996 |
| 21371 | Onyx Industries LTD, Inc. | Wichita Falls, TX 76308 | Oil & Gas Operator | Aug 2003 |
| 21372 | Onyx Int'L Exploration LLC | | Oil & Gas Operator | Dec 2015 |
| 21373 | Onyx Producing Company, Inc. | Pampa, TX 79066 | Oil & Gas Operator | Mar 2008 |
| 21374 | Onyx Properties Corp | Oklahoma City, OK 73114 | Oil & Gas Operator | May 2006 |
| 21375 | Onyxx Energy LLC | | Oil & Gas Operator | Mar 2017 |
| 21376 | Onyxx Oil Corpor | | Oil Operator | Jul 1992 |
| 21377 | Oolite Energy Corp | Amarillo, TX 79105 | Oil & Gas Operator | Apr 2022 |
| 21378 | Oonk, Harvey D. | Clymer, NY 14724 | Gas Operator | Dec 2023 |
| 21379 | Opal Energy, Inc. | Katy, TX 77494 | Oil & Gas Operator | Jun 2009 |
| 21380 | Opal Oil Inc. | | Oil Operator | Sep 2021 |
| 21381 | Opal Operating Company LLC | Oklahoma City, OK 73142 | Oil & Gas Operator | May 2025 |
| 21382 | Opal Resources Operating Co.,LLC | Cypress, TX 77429 | Oil & Gas Operator | Jan 2019 |
| 21383 | Opco LLC | Chase, KS 67524 | Oil Operator | Dec 2019 |
| 21384 | Opco Oil & Gas Co. | Dallas, TX 75231 | Oil & Gas Operator | Aug 2003 |
| 21385 | Opdycke Lease Partners, A General Partnership | Russell, KS 67665 | Oil Operator | Jan 2025 |
| 21386 | Opef Partnership, A General Partnership | Overland Park, KS 66221 | Oil Operator | Dec 2011 |
| 21387 | Open Door Holdings Inc | Surprise, AZ 85387-2015 | Oil & Gas Operator | Feb 2024 |
| 21388 | Open Door Productions Inc | Muskogee, OK 74401-1032 | Oil & Gas Operator | Apr 2020 |
| 21389 | Open Flow Gas Supply Corp | Du Bois, PA 15801-2442 | Oil & Gas Operator | Dec 2024 |
| 21390 | Open Range Energy LLC | Jones, OK 73049-8744 | Oil & Gas Operator | Mar 2025 |
| 21391 | Operating Engineers Local 17 Training Fund | Lake VIew, NY 14085 | Gas Operator | Dec 2023 |
| 21392 | Operator Unknown | Charleston, WV 25304-0000 | Oil & Gas Operator | Dec 2021 |
| 21393 | Opes Production Inc | Buffalo, WY 82834 | Gas Operator | Mar 2015 |
| 21394 | Opex Energy, LLC | Houston, TX 77042 | Oil & Gas Operator | Mar 2008 |
| 21395 | Opmi Operating Company | Houston, TX 77057 | Oil & Gas Operator | Jun 2008 |
| 21396 | Ops Group Limited | Houston, TX 77060 | Oil & Gas Operator | Jun 2014 |
| 21397 | Optima Conservation Resources Exploration LLC | | Oil & Gas Operator | Mar 2025 |
| 21398 | Optima Exploration LLC | Tulsa, OK 74116-5664 | Oil & Gas Operator | Mar 2015 |
| 21399 | Optimistic Oil Co. | | Oil & Gas Operator | Dec 1991 |
| 21400 | Optimum Exploration LLC | Dallas, TX 75240 | Oil & Gas Operator | May 2025 |