| 21201 | Onshore, L.L.C. | Wichita, KS 67205 | Oil & Gas Operator | Dec 2009 |
| 21202 | Onyx Energy Corporation | Oklahoma City, OK 73157 | Oil & Gas Operator | May 1994 |
| 21203 | Onyx Energy Dev Of Texas Inc. | | Oil Operator | Dec 1996 |
| 21204 | Onyx Energy Of Texas Inc. | | Oil Operator | Dec 1996 |
| 21205 | Onyx Industries LTD, Inc. | Wichita Falls, TX 76308 | Oil & Gas Operator | Aug 2003 |
| 21206 | Onyx Int'L Exploration LLC | | Oil & Gas Operator | Dec 2015 |
| 21207 | Onyx Producing Company, Inc. | Pampa, TX 79066 | Oil & Gas Operator | Mar 2008 |
| 21208 | Onyx Properties Corp | Oklahoma City, OK 73114 | Oil & Gas Operator | May 2006 |
| 21209 | Onyxx Energy LLC | | Oil & Gas Operator | Mar 2017 |
| 21210 | Onyxx Oil Corpor | | Oil Operator | Jul 1992 |
| 21211 | Oolite Energy Corp | Amarillo, TX 79105 | Oil & Gas Operator | Apr 2022 |
| 21212 | Oonk, Harvey D. | Clymer, NY 14724 | Gas Operator | Dec 2024 |
| 21213 | Opal Energy, Inc. | Katy, TX 77494 | Oil & Gas Operator | Jun 2009 |
| 21214 | Opal Oil Inc. | | Oil Operator | Sep 2021 |
| 21215 | Opal Operating Company LLC | Edmond, OK 73013 | Oil & Gas Operator | Jul 2025 |
| 21216 | Opal Resources Operating Co.,LLC | Cypress, TX 77429 | Oil & Gas Operator | Jan 2019 |
| 21217 | Opco LLC | Chase, KS 67524 | Oil Operator | Dec 2019 |
| 21218 | Opco Oil & Gas Co. | Dallas, TX 75231 | Oil & Gas Operator | Aug 2003 |
| 21219 | Opdycke Lease Partners, A General Partnership | Russell, KS 67665 | Oil Operator | Mar 2025 |
| 21220 | Opef Partnership, A General Partnership | Overland Park, KS 66221 | Oil Operator | Dec 2011 |
| 21221 | Open Door Holdings Inc | Surprise, AZ 85387-2015 | Oil & Gas Operator | Feb 2024 |
| 21222 | Open Door Productions Inc | Muskogee, OK 74401-1032 | Oil & Gas Operator | Apr 2020 |
| 21223 | Open Flow Gas Supply Corp | Du Bois, PA 15801-2442 | Oil & Gas Operator | Dec 2024 |
| 21224 | Open Range Energy LLC | Jones, OK 73049-8744 | Oil & Gas Operator | Mar 2025 |
| 21225 | Operating Engineers Local 17 Training Fund | Lake VIew, NY 14085 | Gas Operator | Dec 2024 |
| 21226 | Operator Unknown | Charleston, WV 25304-0000 | Oil & Gas Operator | Dec 2021 |
| 21227 | Opes Production Inc | Buffalo, WY 82834 | Gas Operator | Mar 2015 |
| 21228 | Opex Energy, LLC | Houston, TX 77042 | Oil & Gas Operator | Mar 2008 |
| 21229 | Opmi Operating Company | Houston, TX 77057 | Oil & Gas Operator | Jun 2008 |
| 21230 | Ops Group Limited | Houston, TX 77060 | Oil & Gas Operator | Jun 2014 |
| 21231 | Optima Conservation Resources Exploration LLC | | Oil & Gas Operator | Apr 2025 |
| 21232 | Optima Exploration LLC | Tulsa, OK 74116-5664 | Oil & Gas Operator | Mar 2015 |
| 21233 | Optimistic Oil Co. | | Oil & Gas Operator | Dec 1991 |
| 21234 | Optimum Exploration LLC | Dallas, TX 75240 | Oil & Gas Operator | Jul 2025 |
| 21235 | Opubco Resources Of TX Inc | Dallas, TX 75231 | Oil & Gas Operator | Sep 2005 |
| 21236 | Ora Oil Company | | Oil & Gas Operator | May 2017 |
| 21237 | Oracle Oil, LLC | | Oil & Gas Operator | Jul 2013 |
| 21238 | Oracle Resources Oklahoma LP | Dallas, TX 75240-5751 | Oil & Gas Operator | Feb 2008 |
| 21239 | Orange Petroleum Co. | Orangefield, TX 77639 | Oil & Gas Operator | May 1995 |
| 21240 | Orangefield East Corp | Dallas, TX 75382 | Oil Operator | Jul 2025 |
| 21241 | Orangefield Operating Corporation | Dallas, TX 75382 | Oil Operator | Jul 2025 |
| 21242 | Orason Resources Inc | Tulsa, OK 74169-1225 | Oil & Gas Operator | Nov 2006 |
| 21243 | Orb Exploration, L.L.C. | | Oil & Gas Operator | Jun 2017 |
| 21244 | Orbis Energy, L.L.C. | Austin, TX 78746 | Oil & Gas Operator | Oct 2001 |
| 21245 | Orbit Crude, Inc. | Midland, TX 79710 | Oil & Gas Operator | Jul 2025 |
| 21246 | Orbit Enterprises, Inc. | Lovington, NM 88260 | Oil & Gas Operator | Mar 2015 |
| 21247 | Orbit Gas Transmission, Inc | Owensboro, KY 42303 | Oil & Gas Operator | Dec 2023 |
| 21248 | Orbit Petroleum, Inc. | Irving, TX 75038 | Oil & Gas Operator | Sep 2010 |
| 21249 | Orbitron Operating Corp. | Fort Worth, TX 76102 | Oil & Gas Operator | Dec 1995 |
| 21250 | Orbrie Luman | Odessa, TX 79761 | Oil & Gas Operator | May 2025 |
| 21251 | Orca Operating Company LLC | Houston, TX 77056 | Oil & Gas Operator | May 2025 |
| 21252 | Oren Stone | Erick, OK 73645-4542 | Gas Operator | Jun 2022 |
| 21253 | Oretta Holdings LLC | Houston, TX 77010 | Oil & Gas Operator | Jul 2025 |
| 21254 | Organic Energy Company LLC | | Oil & Gas Operator | Jun 2025 |
| 21255 | Origin Prod Co Gonzales Prop LLC | New Braunfels, TX 78132 | Oil & Gas Operator | Jul 2025 |
| 21256 | Origin Production Company, Inc. | New Braunfels, TX 78132 | Oil & Gas Operator | Jul 2025 |
| 21257 | Origin Production Group LLC | Luling, TX 78648 | Oil Operator | Jul 2025 |
| 21258 | Oringderff, Alma Oil Properties | Dallas, TX 75225 | Oil & Gas Operator | Mar 2012 |
| 21259 | Oriole Operating LLC | Wichita Falls, TX 76308 | Oil Operator | Jul 2025 |
| 21260 | Orion Energen Inc. | Austin, TX 78731 | Oil & Gas Operator | Jul 2023 |
| 21261 | Orion Energy Corp | MT Vernon, IL 62864 | Oil & Gas Operator | Dec 1984 |
| 21262 | Orion Energy Partners LP | Denver, CO 80202 | Oil & Gas Operator | Nov 2010 |
| 21263 | Orion Exploration LLC | Tulsa, OK 74105-5153 | Oil & Gas Operator | Apr 2015 |
| 21264 | Orion Exploration Partners LLC | Tulsa, OK 74105-5153 | Oil & Gas Operator | Apr 2025 |
| 21265 | Orion Oil & Gas Prop | Roswell, NM 88202 | Oil & Gas Operator | Apr 1998 |
| 21266 | Orion Oil & Gas Properties | Amarillo, TX 79109 | Gas Operator | Oct 2000 |
| 21267 | Orion Oil & Gas, LLC | Houston, TX 77042 | Oil & Gas Operator | Oct 2007 |
| 21268 | Orion Oil And Gas Corporation | Houston, TX 77082 | Oil & Gas Operator | Jul 2025 |
| 21269 | Orion Petro Corp | MT Vernon, IL 62864 | Oil & Gas Operator | Dec 2016 |
| 21270 | Orisol Oil Co. | Houston, TX 77206 | Oil Operator | Jun 2000 |
| 21271 | Orla Petco Inc & Hopi Drilling Co | Midland, TX 79702 | Oil Operator | Sep 2004 |
| 21272 | Orla Petco, Inc. | Midland, TX 79708 | Oil & Gas Operator | Jul 2025 |
| 21273 | Orland Oil & Gas LLC | FT Lauderdale, FL 33305 | Oil Operator | Aug 2024 |
| 21274 | Orleans Exploration Co., Inc. | | Oil & Gas Operator | Aug 1990 |
| 21275 | Orloski John C | Bartlesville, OK 74006 | Oil & Gas Operator | Apr 2025 |
| 21276 | Ormand, Don R. | Midland, TX 79705 | Oil & Gas Operator | Jan 2016 |
| 21277 | Oro Negro Inc. | | Oil & Gas Operator | Dec 2004 |
| 21278 | Oro Resources, LLC | Houston, TX 77024 | Oil & Gas Operator | Jul 2025 |
| 21279 | Orr Energy LLC | | Oil & Gas Operator | Nov 2012 |
| 21280 | Orr Production Company | Austin, TX 78746 | Oil & Gas Operator | Dec 2000 |
| 21281 | Orr Robert W Jr | Zanesville, OH 43702-2683 | Oil & Gas Operator | Dec 2023 |
| 21282 | Orr, Jr., Donald R. | Batavia, NY 14020 | Gas Operator | Dec 2024 |
| 21283 | Orr, Robert M. | Monahans, TX 79756 | Oil & Gas Operator | Oct 1998 |
| 21284 | Orsburn, Wade Inc. | Gainesville, TX 76240 | Oil & Gas Operator | Nov 2002 |
| 21285 | Orson Leasing & Supply | Rockdale, TX 76567 | Oil & Gas Operator | Dec 2006 |
| 21286 | Orth Oil Company, Inc. | Cisco, TX 76437 | Oil & Gas Operator | Jul 2025 |
| 21287 | Orville S Slaughter Jr | Denver, CO 80205 | Oil & Gas Operator | Aug 2000 |
| 21288 | Orwig Oil Company Inc | Bradenton, FL 34212 | Oil & Gas Operator | Dec 2022 |
| 21289 | Orx Resources, Inc. | | Oil & Gas Operator | Dec 2009 |
| 21290 | Orx Resources, L.L.C. | Houston, TX 77067 | Oil & Gas Operator | Jul 2025 |
| 21291 | Oryx Energy Comp | | Oil & Gas Operator | Apr 1991 |
| 21292 | Oryx Energy Company | Dallas, TX 75221 | Oil & Gas Operator | May 2002 |
| 21293 | Os&S Operating Inc. | Electra, TX 76360 | Oil & Gas Operator | Jul 2025 |
| 21294 | Osa Oil & Gas LLC | Tulsa, OK 74131 | Oil & Gas Operator | Aug 2023 |
| 21295 | Osage Energy Resources LLC | Bartlesville, OK 74005-2527 | Oil & Gas Operator | Apr 2025 |
| 21296 | Osage Energy, LLC | Colony, KS 66015 | Oil Operator | Nov 2023 |
| 21297 | Osage Exploration & Development Inc | San Diego, CA 92131-3807 | Oil & Gas Operator | Oct 2016 |
| 21298 | Osage Hot Oil Service | Newcastle, WY 82701 | Oil & Gas Operator | Jul 1997 |
| 21299 | Osage Oil & Transportation Inc | Cleveland, OK 74020 | Oil & Gas Operator | Nov 2000 |
| 21300 | Osage Operating Company LLC | Seattle, WA 98133 | Oil Operator | May 2006 |