| 21301 | Oneok Resources Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 21302 | Onexxx Prod & Exploration Corp | Jeannette, PA 15644-9691 | Gas Operator | Dec 2024 |
| 21303 | Onnen, Gerhard E. | Yates Center, KS 66783 | Oil Operator | Feb 2002 |
| 21304 | Onpoint Oil & Gas LLC | Oklahoma City, OK 73170-4848 | Oil & Gas Operator | Mar 2025 |
| 21305 | Onshore Exp Cor-La Nat Res Inc | | Oil & Gas Operator | Oct 1978 |
| 21306 | Onshore Pipeline Const Co Inc | | Oil & Gas Operator | Aug 1998 |
| 21307 | Onshore Royalties LLC | Houston, TX 77269 | Oil & Gas Operator | Apr 2025 |
| 21308 | Onshore, L.L.C. | Wichita, KS 67205 | Oil & Gas Operator | Dec 2009 |
| 21309 | Onyx Energy Corporation | Oklahoma City, OK 73157 | Oil & Gas Operator | May 1994 |
| 21310 | Onyx Energy Dev Of Texas Inc. | | Oil Operator | Dec 1996 |
| 21311 | Onyx Energy Of Texas Inc. | | Oil Operator | Dec 1996 |
| 21312 | Onyx Industries LTD, Inc. | Wichita Falls, TX 76308 | Oil & Gas Operator | Aug 2003 |
| 21313 | Onyx Int'L Exploration LLC | | Oil & Gas Operator | Dec 2015 |
| 21314 | Onyx Producing Company, Inc. | Pampa, TX 79066 | Oil & Gas Operator | Mar 2008 |
| 21315 | Onyx Properties Corp | Oklahoma City, OK 73114 | Oil & Gas Operator | May 2006 |
| 21316 | Onyxx Energy LLC | | Oil & Gas Operator | Mar 2017 |
| 21317 | Onyxx Oil Corpor | | Oil Operator | Jul 1992 |
| 21318 | Oolite Energy Corp | Amarillo, TX 79105 | Oil & Gas Operator | Apr 2022 |
| 21319 | Oonk, Harvey D. | Clymer, NY 14724 | Gas Operator | Dec 2023 |
| 21320 | Opal Energy, Inc. | Katy, TX 77494 | Oil & Gas Operator | Jun 2009 |
| 21321 | Opal Oil Inc. | | Oil Operator | Sep 2021 |
| 21322 | Opal Operating Company LLC | Oklahoma City, OK 73142 | Oil & Gas Operator | Jun 2025 |
| 21323 | Opal Resources Operating Co.,LLC | Cypress, TX 77429 | Oil & Gas Operator | Jan 2019 |
| 21324 | Opco LLC | Chase, KS 67524 | Oil Operator | Dec 2019 |
| 21325 | Opco Oil & Gas Co. | Dallas, TX 75231 | Oil & Gas Operator | Aug 2003 |
| 21326 | Opdycke Lease Partners, A General Partnership | Russell, KS 67665 | Oil Operator | Feb 2025 |
| 21327 | Opef Partnership, A General Partnership | Overland Park, KS 66221 | Oil Operator | Dec 2011 |
| 21328 | Open Door Holdings Inc | Surprise, AZ 85387-2015 | Oil & Gas Operator | Feb 2024 |
| 21329 | Open Door Productions Inc | Muskogee, OK 74401-1032 | Oil & Gas Operator | Apr 2020 |
| 21330 | Open Flow Gas Supply Corp | Du Bois, PA 15801-2442 | Oil & Gas Operator | Dec 2024 |
| 21331 | Open Range Energy LLC | Jones, OK 73049-8744 | Oil & Gas Operator | Mar 2025 |
| 21332 | Operating Engineers Local 17 Training Fund | Lake VIew, NY 14085 | Gas Operator | Dec 2023 |
| 21333 | Operator Unknown | Charleston, WV 25304-0000 | Oil & Gas Operator | Dec 2021 |
| 21334 | Opes Production Inc | Buffalo, WY 82834 | Gas Operator | Mar 2015 |
| 21335 | Opex Energy, LLC | Houston, TX 77042 | Oil & Gas Operator | Mar 2008 |
| 21336 | Opmi Operating Company | Houston, TX 77057 | Oil & Gas Operator | Jun 2008 |
| 21337 | Ops Group Limited | Houston, TX 77060 | Oil & Gas Operator | Jun 2014 |
| 21338 | Optima Conservation Resources Exploration LLC | | Oil & Gas Operator | Apr 2025 |
| 21339 | Optima Exploration LLC | Tulsa, OK 74116-5664 | Oil & Gas Operator | Mar 2015 |
| 21340 | Optimistic Oil Co. | | Oil & Gas Operator | Dec 1991 |
| 21341 | Optimum Exploration LLC | Dallas, TX 75240 | Oil & Gas Operator | Jun 2025 |
| 21342 | Opubco Resources Of TX Inc | Dallas, TX 75231 | Oil & Gas Operator | Sep 2005 |
| 21343 | Ora Oil Company | | Oil & Gas Operator | May 2017 |
| 21344 | Oracle Oil, LLC | | Oil & Gas Operator | Jul 2013 |
| 21345 | Oracle Resources Oklahoma LP | Dallas, TX 75240-5751 | Oil & Gas Operator | Feb 2008 |
| 21346 | Orange Petroleum Co. | Orangefield, TX 77639 | Oil & Gas Operator | May 1995 |
| 21347 | Orangefield Operating Corporation | Dallas, TX 75382 | Oil Operator | Jun 2025 |
| 21348 | Orason Resources Inc | Tulsa, OK 74169-1225 | Oil & Gas Operator | Nov 2006 |
| 21349 | Orb Exploration, L.L.C. | | Oil & Gas Operator | Jun 2017 |
| 21350 | Orbis Energy, L.L.C. | Austin, TX 78746 | Oil & Gas Operator | Oct 2001 |
| 21351 | Orbit Crude, Inc. | Midland, TX 79710 | Oil & Gas Operator | Jun 2025 |
| 21352 | Orbit Enterprises, Inc. | Lovington, NM 88260 | Oil & Gas Operator | Mar 2015 |
| 21353 | Orbit Gas Transmission, Inc | Owensboro, KY 42303 | Oil & Gas Operator | Dec 2023 |
| 21354 | Orbit Petroleum, Inc. | Irving, TX 75038 | Oil & Gas Operator | Sep 2010 |
| 21355 | Orbitron Operating Corp. | Fort Worth, TX 76102 | Oil & Gas Operator | Dec 1995 |
| 21356 | Orbrie Luman | Odessa, TX 79761 | Oil & Gas Operator | May 2025 |
| 21357 | Orca Operating Company LLC | Houston, TX 77056 | Oil & Gas Operator | Apr 2025 |
| 21358 | Oren Stone | Erick, OK 73645-4542 | Gas Operator | Jun 2022 |
| 21359 | Oretta Holdings LLC | Houston, TX 77010 | Oil & Gas Operator | Jun 2025 |
| 21360 | Organic Energy Company LLC | | Oil & Gas Operator | May 2025 |
| 21361 | Origin Prod Co Gonzales Prop LLC | New Braunfels, TX 78132 | Oil & Gas Operator | Jun 2025 |
| 21362 | Origin Production Company, Inc. | New Braunfels, TX 78132 | Oil & Gas Operator | Jun 2025 |
| 21363 | Origin Production Group LLC | Luling, TX 78648 | Oil Operator | Jun 2025 |
| 21364 | Oringderff, Alma Oil Properties | Dallas, TX 75225 | Oil & Gas Operator | Mar 2012 |
| 21365 | Oriole Operating LLC | Wichita Falls, TX 76308 | Oil Operator | Jun 2025 |
| 21366 | Orion Energen Inc. | Austin, TX 78731 | Oil & Gas Operator | Jul 2023 |
| 21367 | Orion Energy Corp | MT Vernon, IL 62864 | Oil & Gas Operator | Dec 1984 |
| 21368 | Orion Energy Partners LP | Denver, CO 80202 | Oil & Gas Operator | Nov 2010 |
| 21369 | Orion Exploration LLC | Tulsa, OK 74105-5153 | Oil & Gas Operator | Apr 2015 |
| 21370 | Orion Exploration Partners LLC | Tulsa, OK 74105-5153 | Oil & Gas Operator | Jan 2025 |
| 21371 | Orion Oil & Gas Prop | Roswell, NM 88202 | Oil & Gas Operator | Apr 1998 |
| 21372 | Orion Oil & Gas Properties | Amarillo, TX 79109 | Gas Operator | Oct 2000 |
| 21373 | Orion Oil & Gas, LLC | Houston, TX 77042 | Oil & Gas Operator | Oct 2007 |
| 21374 | Orion Oil And Gas Corporation | Houston, TX 77082 | Oil & Gas Operator | Jun 2025 |
| 21375 | Orion Petro Corp | MT Vernon, IL 62864 | Oil & Gas Operator | Dec 2016 |
| 21376 | Orisol Oil Co. | Houston, TX 77206 | Oil Operator | Jun 2000 |
| 21377 | Orla Petco Inc & Hopi Drilling Co | Midland, TX 79702 | Oil Operator | Sep 2004 |
| 21378 | Orla Petco, Inc. | Midland, TX 79702 | Oil & Gas Operator | Jun 2025 |
| 21379 | Orland Oil & Gas LLC | FT Lauderdale, FL 33305 | Oil Operator | Jun 2025 |
| 21380 | Orleans Exploration Co., Inc. | | Oil & Gas Operator | Aug 1990 |
| 21381 | Orloski John C | Bartlesville, OK 74006 | Oil & Gas Operator | Mar 2025 |
| 21382 | Ormand, Don R. | Midland, TX 79705 | Oil & Gas Operator | Jan 2016 |
| 21383 | Oro Negro Inc. | | Oil & Gas Operator | Dec 2004 |
| 21384 | Oro Resources, LLC | Dallas, TX 75219 | Oil & Gas Operator | Jun 2025 |
| 21385 | Orr Energy LLC | | Oil & Gas Operator | Nov 2012 |
| 21386 | Orr Production Company | Austin, TX 78746 | Oil & Gas Operator | Dec 2000 |
| 21387 | Orr Robert W Jr | Zanesville, OH 43702-2683-2683 | Oil & Gas Operator | Dec 2023 |
| 21388 | Orr, Jr., Donald R. | Batavia, NY 14020 | Gas Operator | Dec 2023 |
| 21389 | Orr, Robert M. | Monahans, TX 79756 | Oil & Gas Operator | Oct 1998 |
| 21390 | Orsburn, Wade Inc. | Gainesville, TX 76240 | Oil & Gas Operator | Nov 2002 |
| 21391 | Orson Leasing & Supply | Rockdale, TX 76567 | Oil & Gas Operator | Dec 2006 |
| 21392 | Orth Oil Company, Inc. | Cisco, TX 76437 | Oil & Gas Operator | Jun 2025 |
| 21393 | Orville S Slaughter Jr | Denver, CO 80205 | Oil & Gas Operator | Aug 2000 |
| 21394 | Orwig Oil Company Inc | Bradenton, FL 34212 | Oil & Gas Operator | Dec 2022 |
| 21395 | Orx Resources, Inc. | | Oil & Gas Operator | Dec 2009 |
| 21396 | Orx Resources, L.L.C. | Houston, TX 77067 | Oil & Gas Operator | Jun 2025 |
| 21397 | Oryx Energy Comp | | Oil & Gas Operator | Apr 1991 |
| 21398 | Oryx Energy Company | Dallas, TX 75221 | Oil & Gas Operator | May 2002 |
| 21399 | Os&S Operating Inc. | Electra, TX 76360 | Oil & Gas Operator | Jun 2025 |
| 21400 | Osa Oil & Gas LLC | Tulsa, OK 74131 | Oil & Gas Operator | Aug 2023 |