| 401 | Terry Petroleum Company | Houston, TX 77270 | Oil & Gas Operator | Dec 1997 |
| 402 | Tex-Lee Operating Company | Giddings, TX 78942 | Oil & Gas Operator | May 2025 |
| 403 | Tex-Oak, Inc. | Oklahoma City, OK 73155 | Oil & Gas Operator | Dec 1995 |
| 404 | Texas Crude, Inc. | Houston, TX 77256 | Oil & Gas Operator | Oct 1995 |
| 405 | Texas Energy Reserves, Inc | New Braunfels, TX 78130 | Oil & Gas Operator | Jun 1996 |
| 406 | Texas Onshore Energy, Inc. | Austin, TX 78704 | Oil & Gas Operator | May 2025 |
| 407 | Texas Refining, Inc. | Houston, TX 77057 | Oil & Gas Operator | Aug 2003 |
| 408 | Texas Vanguard Oil Company | Austin, TX 78720 | Oil & Gas Operator | Jan 2014 |
| 409 | Tipperary Oil & Gas Corp | Denver, CO 80202 | Oil & Gas Operator | May 2014 |
| 410 | Tiza Operating Company | Austin, TX 78716 | Oil & Gas Operator | Jan 2000 |
| 411 | TK Drilling Corp. | Tulsa, OK 74133 | Oil & Gas Operator | Feb 2025 |
| 412 | Torch Energy Services, Inc. | Houston, TX 77010 | Oil & Gas Operator | Sep 2011 |
| 413 | Torch Operating Company | Houston, TX 77010 | Oil & Gas Operator | Mar 2015 |
| 414 | Tri-C Resources, Inc. | Houston, TX 77024 | Oil & Gas Operator | Aug 2009 |
| 415 | Tri-C Resources, LLC | Houston, TX 77024 | Oil & Gas Operator | May 2025 |
| 416 | Trinity Resources, Inc. | Houston, TX 77277 | Oil & Gas Operator | May 2020 |
| 417 | Trivista Operating LLC | Giddings, TX 78942 | Oil & Gas Operator | May 2025 |
| 418 | Trump Energy | Austin, TX 78734 | Oil & Gas Operator | Mar 2008 |
| 419 | Tsar Energy, LLC | Dallas, TX 75205 | Oil & Gas Operator | May 2025 |
| 420 | TT Operating, LLC | Kilgore, TX 75663 | Oil & Gas Operator | May 2025 |
| 421 | Two Bit Operating Company LLC | Fort Worth, TX 76110 | Oil & Gas Operator | May 2025 |
| 422 | Txco Resources Inc. | San Antonio, TX 78280 | Oil & Gas Operator | May 2025 |
| 423 | U. S. Operating, Inc. | Dallas, TX 75252 | Oil & Gas Operator | May 2025 |
| 424 | U.S.A. Plugging Company | Pearsall, TX 78061 | Oil & Gas Operator | May 2025 |
| 425 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 426 | Union Pacific Austin Chalk Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Jan 2001 |
| 427 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Sep 2002 |
| 428 | Unit Petroleum Company | Tulsa, OK 74170 | Oil & Gas Operator | May 2025 |
| 429 | United Energy Operating, LLC | Edmond, OK 73083 | Oil & Gas Operator | May 2025 |
| 430 | United Oil & Minerals, Inc. | Austin, TX 78746 | Oil & Gas Operator | Jan 2001 |
| 431 | United Resources LP | Austin, TX 78746 | Oil & Gas Operator | Oct 2011 |
| 432 | Upland Resources LLC | Canadian, TX 79014 | Oil & Gas Operator | May 2025 |
| 433 | Usfg Oil & Gas, Inc. | Dallas, TX 75231 | Oil & Gas Operator | Dec 2005 |
| 434 | Valence Operating Company | Kingwood, TX 77339 | Oil & Gas Operator | May 2025 |
| 435 | Verdun Oil & Gas LLC | Houston, TX 77024 | Oil & Gas Operator | May 2025 |
| 436 | Vintage Petroleum, Inc. | Houston, TX 77046 | Oil & Gas Operator | Feb 2025 |
| 437 | Vomela Resources Inc. | Flatonia, TX 78941 | Oil & Gas Operator | May 2025 |
| 438 | Warrior Resources Inc. | Mexia, TX 76667 | Oil & Gas Operator | May 2025 |
| 439 | Waters Eng. & Operating, Inc. | Corpus Chrsti, TX 78471 | Oil & Gas Operator | Sep 2013 |
| 440 | WCS Oil & Gas Corporation | Dallas, TX 75209 | Oil & Gas Operator | Aug 2021 |
| 441 | Weber Energy Corporation | Dallas, TX 75219 | Oil & Gas Operator | Feb 2017 |
| 442 | Westpark Petroleum, Inc. | Austin, TX 78755 | Oil & Gas Operator | May 2025 |
| 443 | Westport Oil & Gas Company LP | The Woodlands, TX 77380 | Oil & Gas Operator | Feb 2007 |
| 444 | Westridge Oil & Gas Properties | Mineral Wells, TX 76068 | Oil & Gas Operator | May 2025 |
| 445 | Whiting Oil And Gas Corporation | Houston, TX 77002 | Oil & Gas Operator | May 2025 |
| 446 | Whiting Petroleum Corporation | Denver, CO 80290 | Oil & Gas Operator | Jan 2025 |
| 447 | Wilco Properties, Inc. | Dallas, TX 75205 | Oil & Gas Operator | Jan 2004 |
| 448 | Wildfire Energy Operating LLC | Houston, TX 77224 | Oil & Gas Operator | May 2025 |
| 449 | Wildhorse Resources MNGT Co, LLC | Oklahoma City, OK 73154 | Oil & Gas Operator | May 2019 |
| 450 | Williams, Clayton Energy, Inc. | Houston, TX 77070 | Oil & Gas Operator | May 2025 |
| 451 | Williams, Clayton Energy, L.L.C | Midland, TX 79705 | Oil & Gas Operator | May 1993 |
| 452 | Williams, Clayton W., Jr., Inc. | Midland, TX 79705 | Oil & Gas Operator | Mar 2008 |
| 453 | Williams-Cody, Inc. | Houston, TX 77060 | Oil & Gas Operator | May 1994 |
| 454 | XTO Energy Inc. | Spring, TX 77389 | Oil & Gas Operator | May 2025 |
| 455 | Yarborough, W. B. | Midland, TX 79701 | Oil & Gas Operator | Nov 1995 |
| 456 | Young, John H., Inc. | Houston, TX 77027 | Oil & Gas Operator | May 2025 |
| 457 | Zarvona Energy LLC | Houston, TX 77002 | Oil & Gas Operator | May 2025 |
| 458 | Zaza Energy, LLC | Houston, TX 77010 | Oil & Gas Operator | May 2025 |
| 459 | Zinn Petroleum Co. | Houston, TX 77024 | Oil & Gas Operator | Nov 2021 |