| 21201 | Old Dominion Oil Corporation | Oklahoma City, OK 73107 | Oil & Gas Operator | Apr 2009 |
| 21202 | Old Field Associates | | Oil & Gas Operator | Apr 2025 |
| 21203 | Old MTN Gas Co Inc | Pleasantville, PA 16341-0329 | Oil & Gas Operator | Dec 2020 |
| 21204 | Old Pine Energy Corporation | Austin, TX 78755 | Oil Operator | Jun 2025 |
| 21205 | Old South Oil LLC | Marietta, OH 45750 | Oil & Gas Operator | Dec 2023 |
| 21206 | Old Timers Oil | Saratoga, TX 77585 | Oil & Gas Operator | Nov 2014 |
| 21207 | Old Timers Oil Company, LLC | Saratoga, TX 77585 | Oil Operator | Aug 2022 |
| 21208 | Old Timers Oil No. 2 Incorporated | Saratoga, TX 77585 | Oil Operator | Jun 2025 |
| 21209 | Old Union Operating Company | Austin, TX 78716 | Oil & Gas Operator | Jun 2025 |
| 21210 | Olde Chautauqua Farms | Portland, NY 14769 | Gas Operator | Dec 2023 |
| 21211 | Older Than Dirt LLC | Palo Pinto, TX 76484 | Oil & Gas Operator | Jun 2025 |
| 21212 | Oldfield Acquisition LP | Austin, TX 78733 | Oil & Gas Operator | Sep 1996 |
| 21213 | Oldfield Operating Corporation | | Oil Operator | Dec 2013 |
| 21214 | Olds Oil Company | Casper, WY 82604 | Oil Operator | Jun 1988 |
| 21215 | Ole Chaparral On Possum Kingdom | Wichita Falls, TX 76307 | Oil & Gas Operator | Dec 1997 |
| 21216 | Ole Crow Operating | Wichita Falls, TX 76308 | Oil Operator | Mar 2025 |
| 21217 | Ole Miss Oil & Gas Inc | New Bremen, OH 45689 | Oil & Gas Operator | Dec 1985 |
| 21218 | Ole, Inc. | Graham, TX 76450 | Oil & Gas Operator | Aug 2003 |
| 21219 | Oleksandr Antonyuk | | Oil & Gas Operator | Dec 2018 |
| 21220 | Oleum Energy LLC | Georgetown, TX 78628 | Oil & Gas Operator | Mar 2025 |
| 21221 | Oleum Exploration, LLC | Brodheadsvill, PA 18322 | Oil & Gas Operator | Mar 2023 |
| 21222 | Oleum Incorporat | | Gas Operator | Dec 1990 |
| 21223 | Oleum Incorporated | | Oil & Gas Operator | Mar 1996 |
| 21224 | Oleum Operating Company, L.C. | Longview, TX 75606 | Oil & Gas Operator | Dec 2021 |
| 21225 | Oleum Operating La LLC | | Oil & Gas Operator | Nov 2022 |
| 21226 | Oleum Partners, LLC | Frisco, TX 75034 | Oil & Gas Operator | Jun 2025 |
| 21227 | Olia Oil & Gas Services LLC | Cedar Park, TX 78630-2049 | Oil & Gas Operator | Aug 2022 |
| 21228 | Oliditt Corporation | | Gas Operator | Mar 2022 |
| 21229 | Oliditt Production Inc. | | Gas Operator | Sep 1998 |
| 21230 | Olifant Energy LLC | Tulsa, OK 74119 | Oil & Gas Operator | Jun 2019 |
| 21231 | Olipdp II, LLC | Lafayette, LA 70503 | Oil & Gas Operator | Jun 2025 |
| 21232 | Oliphant Gertrud | Holdenville, OK 74848-0849 | Oil Operator | Aug 2013 |
| 21233 | Oliphant Operating Co,LTD,LLC | | Oil Operator | Mar 2025 |
| 21234 | Olive Oil & Gas | Ellensboro, WV 26346 | Oil & Gas Operator | Dec 2021 |
| 21235 | Olive Oil & Gas Inc | Jennings, OK 74052 | Oil & Gas Operator | Mar 2025 |
| 21236 | Oliver Oil & Gas | Midland, TX 79702 | Oil & Gas Operator | Jun 2025 |
| 21237 | Olmos Partners, Inc. | Boerne, TX 78006 | Oil & Gas Operator | Jun 2025 |
| 21238 | Olney Oil LLC | Boerne, TX 78006 | Oil Operator | Jun 2025 |
| 21239 | Olney Properties, Inc. | Wichita Falls, TX 76307 | Oil & Gas Operator | Sep 2003 |
| 21240 | Olsan Brothers, Inc. | Dallas, TX 75251 | Oil & Gas Operator | Apr 1994 |
| 21241 | Olsen Energy Inc. | Boerne, TX 78006 | Oil & Gas Operator | Jun 2025 |
| 21242 | Olson D Producti | | Oil Operator | Jul 1994 |
| 21243 | Olson, S. A. | Kenedy, TX 78119 | Oil & Gas Operator | Aug 1994 |
| 21244 | Olson-Anderson Lease | | Oil Operator | Mar 2018 |
| 21245 | Oltex Production | Idalou, TX 79329 | Oil & Gas Operator | Jun 2025 |
| 21246 | Olympia Oil Inc | Edmond, OK 73083-7088 | Oil & Gas Operator | Jul 2020 |
| 21247 | Olympic Exploration & Production Co | Norman, OK 73072 | Oil Operator | May 2003 |
| 21248 | Olympic Exploration Inc | Denver, CO 80202 | Oil & Gas Operator | Jul 2004 |
| 21249 | Olympic Natural Gas Company | | Oil & Gas Operator | Oct 1990 |
| 21250 | Olympic Oil & Gas Co., Inc. | | Oil Operator | Apr 1991 |
| 21251 | Olympic Oil, Inc. | Hutchinson, KS 67502 | Oil & Gas Operator | Feb 2025 |
| 21252 | Olympic Petroleu | | Oil & Gas Operator | Jul 1993 |
| 21253 | Olympic Petroleum Company | Tulsa, OK 74114 | Oil & Gas Operator | Jun 1998 |
| 21254 | Olympic Production Company | | Oil & Gas Operator | Jul 1994 |
| 21255 | Olympic Resources Co | Wooster, OH 44691 | Oil & Gas Operator | Dec 2000 |
| 21256 | Olympus Energy, LLC | Canonsburg, PA 15317 | Gas Operator | Apr 2025 |
| 21257 | Olympus Prop Inc | Franklin Park, IL 60131-1418 | Oil & Gas Operator | Dec 1997 |
| 21258 | Omac Oil & Gas Co | Newark, OH 43055 | Oil & Gas Operator | Dec 1990 |
| 21259 | Omar Operating Company | Midland, TX 79702 | Oil & Gas Operator | Sep 2013 |
| 21260 | Omber Petroleum & Energy Corp. | New Braunfels, TX 78131 | Oil & Gas Operator | Jun 2025 |
| 21261 | Omeara Bros. | | Oil & Gas Operator | Oct 1982 |
| 21262 | Omega Alpha Resources, LLC | Dallas, TX 75219 | Oil Operator | Jun 2025 |
| 21263 | Omega Energy Corp. | Graham, TX 76450 | Oil & Gas Operator | Jun 2025 |
| 21264 | Omega Energy Incorporated | | Oil & Gas Operator | May 1998 |
| 21265 | Omega Energy, LLC | Corpus Chrsti, TX 78418 | Oil & Gas Operator | Jun 2025 |
| 21266 | Omega Enterprise | | Oil Operator | Sep 1990 |
| 21267 | Omega Oil Corp | Lafayette, IN 47903 | Oil & Gas Operator | Dec 1987 |
| 21268 | Omega Operating, Inc. | Odessa, TX 79769 | Oil & Gas Operator | Mar 2001 |
| 21269 | Omega Resources Inc | | Oil & Gas Operator | Nov 1998 |
| 21270 | Omimex Canada, LTD. | Fort Worth, TX 76120-3608 | Oil & Gas Operator | Mar 2025 |
| 21271 | Omimex Energy, Inc. | Fort Worth, TX 76120 | Oil & Gas Operator | Jan 2025 |
| 21272 | Omimex International Corp | Fort Worth, TX 76103-2300 | Oil & Gas Operator | Mar 2025 |
| 21273 | Omimex Petroleum Inc | Fort Worth, TX 76120 | Oil & Gas Operator | Aug 2022 |
| 21274 | Omimex Petroleum Inc (Co) | Newcastle, WY 82701 | Oil & Gas Operator | May 2001 |
| 21275 | Omimex Petroleum Inc (De) | Fort Worth, TX 76120 | Oil & Gas Operator | Aug 2020 |
| 21276 | Omni E & P, Inc. | San Antonio, TX 78229 | Oil Operator | Apr 2010 |
| 21277 | Omni Oil & Gas, Inc. | San Antonio, TX 78229 | Oil & Gas Operator | Oct 2017 |
| 21278 | Omni Operating Company | Osage, WY 82723 | Oil & Gas Operator | Sep 2001 |
| 21279 | Omni Operating Company(A) | Dallas, TX 75370 | Oil & Gas Operator | Jun 2025 |
| 21280 | Omni Petroleum Corporation | Austin, TX 78738 | Oil & Gas Operator | Jun 2025 |
| 21281 | Omr Drilling & Acquisition LLC | Albany, KY 42602 | Oil Operator | Dec 2015 |
| 21282 | On Pointe Operating LLC | Jones, OK 73049 | Oil & Gas Operator | Jun 2025 |
| 21283 | On-Line Oil Inc | Oklahoma City, OK 73105-5208 | Oil & Gas Operator | Mar 2015 |
| 21284 | Onapa Gas Company LLC | Tulsa, OK 74136-7253 | Gas Operator | Nov 2019 |
| 21285 | Onaroll Operating LLC | Levelland, TX 79336 | Oil Operator | Jun 2025 |
| 21286 | Onco Petroleum USA Inc | | Oil Operator | Dec 2009 |
| 21287 | One Epoch Energy, Inc. | Abilene, TX 79604 | Oil & Gas Operator | Mar 2008 |
| 21288 | One Nickel Operating LLC | Westbrook, TX 79565 | Oil Operator | Jun 2025 |
| 21289 | One Source Financial Services Inc. | McAllen, TX 78501 | Gas Operator | Dec 2019 |
| 21290 | One Tec Operating, LLC | Houston, TX 77002 | Oil & Gas Operator | Nov 2007 |
| 21291 | One World Operating, LLC | Tampa, FL 33602 | Oil & Gas Operator | Jun 2025 |
| 21292 | Oneenergy Partners Operating, LLC | Houston, TX 77019 | Oil & Gas Operator | Nov 2018 |
| 21293 | Oneida Energy Corporation | Tulsa, OK 74137 | Oil & Gas Operator | Jul 2003 |
| 21294 | Oneok Bushton Proces | | Gas Operator | Mar 2007 |
| 21295 | Oneok Energy Service | | Gas Operator | Dec 2008 |
| 21296 | Oneok Exploratio | | Oil & Gas Operator | Mar 1995 |
| 21297 | Oneok Exploration Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 21298 | Oneok Field Services Company | Tulsa, OK 74103 | Oil & Gas Operator | Jul 2022 |
| 21299 | Oneok Gas Processing LLC | Tulsa, OK 74103 | Oil & Gas Operator | May 2018 |
| 21300 | Oneok Gas Transportation Co | Tulsa, OK 74121-2089 | Oil & Gas Operator | Oct 2014 |