| 21201 | O'Donnell Oil LLC | | Oil & Gas Operator | Dec 2024 |
| 21202 | O'Donohoe, Jack | Wichita Falls, TX 76301 | Oil & Gas Operator | May 2002 |
| 21203 | O'Gorman, Brendan & Wheeler, Anne | North Collins, NY 14111 | Gas Operator | Dec 2023 |
| 21204 | O'Gorman, Kevin | Eden, NY 14057 | Gas Operator | Dec 2023 |
| 21205 | O'Hare Energy Co | | Oil Operator | Dec 1983 |
| 21206 | O'Hern Morris D | Mounds, OK 74047-5163 | Oil & Gas Operator | Sep 2016 |
| 21207 | O'Leary'S Oil & Gas Inc. | Arcadia, FL 34266 | Oil & Gas Operator | May 2008 |
| 21208 | O'Malley Production Co. Inc. | | Oil & Gas Operator | Mar 1988 |
| 21209 | O'Meara LLC | | Oil & Gas Operator | Oct 2022 |
| 21210 | O'Meara, Inc. | | Oil & Gas Operator | Dec 2006 |
| 21211 | O'Neal Cattle Co. | Pampa, TX 79066 | Gas Operator | Apr 2025 |
| 21212 | O'Neal Oil & Gas Co | Fort Worth, TX 76107-1479 | Oil & Gas Operator | Feb 2025 |
| 21213 | O'Neal Oil Company | Nocona, TX 76255 | Oil & Gas Operator | Apr 2025 |
| 21214 | O'Neal Operating Company | Wichita Falls, TX 76307 | Oil & Gas Operator | Dec 1999 |
| 21215 | O'Neal, Lindell | Nocona, TX 76255 | Oil & Gas Operator | Jan 2025 |
| 21216 | O'Neil Properties LTD | Midland, TX 79702 | Oil & Gas Operator | Jun 2015 |
| 21217 | O'Neil, Pat | Wichita Falls, TX 76308 | Oil & Gas Operator | Nov 2005 |
| 21218 | O'Neill Properties, LTD. | Midland, TX 79702 | Oil & Gas Operator | Apr 2025 |
| 21219 | O'Ryan Oil And Gas | Odessa, TX 79768 | Oil & Gas Operator | Apr 2025 |
| 21220 | O'Sand Production, Inc. | Tomball, TX 77377 | Oil & Gas Operator | Aug 2003 |
| 21221 | O'Sullivan & Scully, Inc. | | Oil & Gas Operator | Oct 1994 |
| 21222 | O'Sullivan Oil & Gas Co., Inc. | Houston, TX 77002 | Oil & Gas Operator | Oct 2000 |
| 21223 | O'Tool Oil & Gas, LLC | Dallas, TX 75219 | Oil & Gas Operator | Apr 2025 |
| 21224 | O. B. And Keith Whatley | | Oil Operator | Jul 1993 |
| 21225 | O. B. Beck | | Oil Operator | Feb 1991 |
| 21226 | O. B. Mobley | | Oil & Gas Operator | Jul 1989 |
| 21227 | O. B. Mobley, Et Al | | Oil Operator | Jul 1989 |
| 21228 | O. B. Whatley | | Oil Operator | Jul 1993 |
| 21229 | O. D. Maybrier | | Oil Operator | Dec 2011 |
| 21230 | O. F. H., Inc. | | Oil Operator | May 1990 |
| 21231 | O. G., Inc. | | Oil & Gas Operator | Nov 1992 |
| 21232 | O. H. B. Inc. | San Angelo, TX 76902 | Oil & Gas Operator | Sep 2019 |
| 21233 | O. H. M. Operating | Pampa, TX 79065 | Oil & Gas Operator | Apr 2025 |
| 21234 | O. O. Cummings | | Gas Operator | Jan 1999 |
| 21235 | O.B. Whatley Oil Company, Inc. | | Oil Operator | Feb 2013 |
| 21236 | O.B., Keith & Owen B. Whatley | | Oil Operator | Jul 1989 |
| 21237 | O.G.O. Refining | Luling, TX 78648 | Oil & Gas Operator | Jun 2013 |
| 21238 | O.G.P. Operating, Inc. | Dallas, TX 75231 | Oil & Gas Operator | Apr 2025 |
| 21239 | O.I.L. Energy, Inc. | | Oil & Gas Operator | Dec 1984 |
| 21240 | O.K. Mikeal Joint Venture | Wilmington, DE 19803 | Oil & Gas Operator | Jun 2012 |
| 21241 | O.T. Oil | Kilgore, TX 75663 | Oil Operator | Apr 2025 |
| 21242 | Oahe Oil Company | Texline, TX 79087 | Oil & Gas Operator | May 2004 |
| 21243 | Oak Dale Drilling Co | Logan, OH 43138-1851-1851 | Oil & Gas Operator | Dec 2015 |
| 21244 | Oak Energy, LLC | Houston, TX 77027 | Oil & Gas Operator | Apr 2025 |
| 21245 | Oak Grove Resources, LLC | | Gas Operator | Jan 2025 |
| 21246 | Oak Hill Petroleum Corporation | Oklahoma City, OK 73116-5627 | Oil & Gas Operator | Feb 2025 |
| 21247 | Oak Hills Drilling & Oper., LLC | Holdenville, OK 74848 | Oil & Gas Operator | May 2013 |
| 21248 | Oak Hills Energy Inc | Holdenville, OK 74848-0470 | Oil & Gas Operator | Sep 2014 |
| 21249 | Oak Prairie Operations, LLC | The Woodlands, TX 77381 | Oil & Gas Operator | Apr 2025 |
| 21250 | Oak Resources Inc | Tulsa, OK 74153 | Oil & Gas Operator | Aug 2013 |
| 21251 | Oak Ridge LLC | Wellsville, KS 66092 | Oil Operator | Dec 2019 |
| 21252 | Oak Tree Natural Res LLC | Oklahoma City, OK 73120-5065 | Oil & Gas Operator | Mar 2015 |
| 21253 | Oak Valley Operating, LLC | The Woodlands, TX 77380 | Oil & Gas Operator | Jun 2015 |
| 21254 | Oak Valley SWD LLC | Enid, OK 73703-4637 | Oil Operator | Aug 2022 |
| 21255 | Oakes Gas Co Inc | Kane, PA 16735-3905 | Gas Operator | Dec 2023 |
| 21256 | Oakfield Energy LLC | | Oil Operator | Jun 2019 |
| 21257 | Oakland Corporation | | Oil & Gas Operator | Dec 1981 |
| 21258 | Oakland Petroleum Oper Co., Inc. | Kilgore, TX 75663 | Oil & Gas Operator | Apr 2025 |
| 21259 | Oakley Oil & Gas, L.L.C. | | Oil & Gas Operator | Mar 2012 |
| 21260 | Oakmont CC | Oakmont, PA 15139-1135 | Gas Operator | Dec 2024 |
| 21261 | Oakmont Oil And Gas | Graham, TX 76450 | Oil Operator | Apr 2025 |
| 21262 | Oakridge Energy, Inc. | Wichita Falls, TX 76302 | Oil & Gas Operator | Apr 2025 |
| 21263 | Oakridge Oil And Gas, LP | Jacksboro, TX 76458 | Oil & Gas Operator | Apr 2025 |
| 21264 | Oaks Petroleum I | | Oil Operator | Jul 1987 |
| 21265 | Oaktree Oil Company | Albany, TX 76430 | Oil & Gas Operator | Apr 2025 |
| 21266 | Oakwood Energy, Inc. | Jourdanton, TX 78026 | Oil & Gas Operator | Mar 2023 |
| 21267 | Oakwood Resources, Inc. | Dallas, TX 75374 | Oil & Gas Operator | May 1998 |
| 21268 | Oasis Energy Resources LLC | Norman, OK 73072-9668 | Oil & Gas Operator | Jan 2025 |
| 21269 | Oasis Operating, Inc. | Lubbock, TX 79404 | Oil & Gas Operator | Nov 2020 |
| 21270 | Oasis Petroleum | | Gas Operator | Feb 1984 |
| 21271 | Oasis Petroleum North America LLC | Houston, TX 77002 | Oil & Gas Operator | Feb 2025 |
| 21272 | Oasis Petroleum Permian LLC | Houston, TX 77002 | Oil & Gas Operator | Apr 2025 |
| 21273 | Oasis Production Co., Inc. | | Oil & Gas Operator | Jun 1988 |
| 21274 | Oast, Thomas H. | Greenville, NC 27835 | Oil Operator | Nov 1985 |
| 21275 | Oates, John Co., Inc. | Stinnett, TX 79083 | Oil & Gas Operator | Apr 2025 |
| 21276 | Obax Oil And Gas LLC | Saint Louis, MO 63131 | Oil Operator | Apr 2025 |
| 21277 | Obele Oil Corporation | Sedona, AZ 86336-5745 | Oil & Gas Operator | May 2017 |
| 21278 | Obele Operating Company LLC | Sedona, AZ 86336-5745 | Oil & Gas Operator | Jan 2025 |
| 21279 | Oberlander Leslie A Jake | Covington, OK 73730 | Oil Operator | Jun 2007 |
| 21280 | Obermiller Clarence Trust | Creston, OH 44217 | Oil & Gas Operator | Dec 1987 |
| 21281 | Obermiller Paul J | Creston, OH 44217 | Oil & Gas Operator | Dec 2014 |
| 21282 | Oblaen Resources LLC | Wallis, TX 77485 | Oil & Gas Operator | Apr 2025 |
| 21283 | Occ Operating Co. | | Oil & Gas Operator | Apr 2019 |
| 21284 | Occidental Energy Company, Inc. | Houston, TX 77282 | Oil & Gas Operator | Jul 2021 |
| 21285 | Occidental Energy Marketing, Inc. | Houston, TX 77227 | Gas Operator | Sep 2015 |
| 21286 | Occidental Energy MKT Inc | Houston, TX 77001 | Oil & Gas Operator | Jan 2011 |
| 21287 | Occidental Of Elk Hills Inc. | | Oil & Gas Operator | Dec 2014 |
| 21288 | Occidental Permian LTD. | Houston, TX 77046 | Oil & Gas Operator | Apr 2025 |
| 21289 | Occidental Petroleum Corporation | | Oil & Gas Operator | Dec 2021 |
| 21290 | Occidental W TX Overthrust, Inc. | Houston, TX 77210 | Oil & Gas Operator | Dec 2021 |
| 21291 | Ocean Energy Inc Ndba Devon Louisiana Corp | | Oil & Gas Operator | Jul 2001 |
| 21292 | Ocean Energy Resources Inc. | Houston, TX 77002 | Oil & Gas Operator | Dec 2024 |
| 21293 | Ocean Energy, Inc. | Houston, TX 77002 | Oil & Gas Operator | Aug 2003 |
| 21294 | Ocfiw Oil Company, Inc. | Hartington, NE 68739 | Oil & Gas Operator | Dec 2009 |
| 21295 | Ochiltree Oil Company | Edmond, OK 73034 | Oil & Gas Operator | Apr 2020 |
| 21296 | Oci LLC | Thermopolis, WY 82443 | Oil Operator | Jan 2024 |
| 21297 | Octagon Resources Corporation | | Oil Operator | Apr 2005 |
| 21298 | Octagon Resources LLC | Norman, OK 73071-1295 | Oil & Gas Operator | May 2015 |
| 21299 | Octane Energy Operating, LLC | Midland, TX 79701 | Oil & Gas Operator | Apr 2025 |
| 21300 | Odebralski, Michael & Connie | Fredonia, NY 14063 | Gas Operator | Dec 2023 |