| 401 | Titan Rock E&P, LLC | Kilgore, TX 75663 | Oil & Gas Operator | Jan 2024 |
| 402 | Tomlinson, Thomas K. Inc. | Port Lavaca, TX 77979 | Oil & Gas Operator | Jul 2003 |
| 403 | Torch Operating Company | Houston, TX 77010 | Oil & Gas Operator | Mar 2015 |
| 404 | Torrent Oil LLC | Houston, TX 77002 | Oil & Gas Operator | May 2025 |
| 405 | Tpet Management Inc. | Dallas, TX 75204 | Oil & Gas Operator | Dec 1997 |
| 406 | Trans-Pecos Resources, Inc. | Houston, TX 77056 | Oil & Gas Operator | May 2025 |
| 407 | Transamerican Natural Gas Corp. | Houston, TX 77032 | Oil & Gas Operator | Aug 2000 |
| 408 | Transtexas Gas Corporation | Houston, TX 77265 | Oil & Gas Operator | Aug 2005 |
| 409 | Tri-Union Development Corp. | Houston, TX 77002 | Oil & Gas Operator | May 2025 |
| 410 | Trinity Resources, Inc. | Houston, TX 77277 | Oil & Gas Operator | May 2020 |
| 411 | Trinity River Operating Company | Oklahoma City, OK 73147 | Oil & Gas Operator | May 2025 |
| 412 | True Oil Company | Casper, WY 82602 | Oil & Gas Operator | Aug 2003 |
| 413 | Tucker Operating Co., Inc. | Victoria, TX 77903 | Oil & Gas Operator | May 2025 |
| 414 | Umc Petroleum Corporation | Houston, TX 77002 | Oil & Gas Operator | Mar 2015 |
| 415 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 416 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Sep 2002 |
| 417 | Union Seaboard Corporation | Houston, TX 77024 | Oil & Gas Operator | Mar 2008 |
| 418 | Universal Petroleum Corporation | Houston, TX 77002 | Oil & Gas Operator | Sep 2002 |
| 419 | Valence Operating Company | Kingwood, TX 77339 | Oil & Gas Operator | May 2025 |
| 420 | Valley Gathering Company | Midland, TX 79702 | Oil & Gas Operator | Feb 1997 |
| 421 | Vandeveer Energy, LLC | Dallas, TX 75225 | Oil & Gas Operator | Jul 2016 |
| 422 | Ventex Operating Corp. | Addison, TX 75001 | Oil & Gas Operator | May 2025 |
| 423 | Veracity Energy LLC | The Woodlands, TX 77380 | Oil & Gas Operator | Aug 2023 |
| 424 | Vintage Petroleum, Inc. | Houston, TX 77046 | Oil & Gas Operator | Feb 2025 |
| 425 | Vintage Petroleum, LLC | Houston, TX 77210 | Oil & Gas Operator | Dec 2019 |
| 426 | Viola Production Inc | Dallas, TX 75251 | Oil & Gas Operator | May 2025 |
| 427 | Wacker Oil Inc | Houston, TX 77002 | Oil & Gas Operator | Aug 1996 |
| 428 | Wagner Oil Company | Fort Worth, TX 76102 | Oil & Gas Operator | May 2025 |
| 429 | Wagner, Duer & Co. | Fort Worth, TX 76102 | Oil & Gas Operator | Jan 1999 |
| 430 | Wainoco Oil & Gas Company | Houston, TX 77024 | Oil & Gas Operator | Dec 2005 |
| 431 | Walker, Tigner | Shreveport, LA 71138 | Oil & Gas Operator | Feb 2005 |
| 432 | Walsh & Watts Inc | Aledo, TX 76008 | Oil & Gas Operator | May 2025 |
| 433 | Walter Oil & Gas Corporation | Houston, TX 77002 | Oil & Gas Operator | May 2025 |
| 434 | Western Energy Group, LLC | Leander, TX 78641 | Oil & Gas Operator | May 2025 |
| 435 | Western Gulf Oil & Gas Inc. | Dallas, TX 75360 | Oil & Gas Operator | Jul 2000 |
| 436 | Western Gulf Oil & Gas, LLC | Bishop, TX 78343 | Oil & Gas Operator | May 2025 |
| 437 | Westland Oil Development Corp. | Conroe, TX 77305 | Oil & Gas Operator | Mar 2008 |
| 438 | WFMMS, Inc. | Batson, TX 77519 | Oil & Gas Operator | May 2025 |
| 439 | White Oak Operating Company LLC | Houston, TX 77077 | Oil & Gas Operator | May 2025 |
| 440 | Whitson, James A., Jr. | Houston, TX 77063 | Oil & Gas Operator | Nov 2011 |
| 441 | Wilbanks Energy Corporation | Houston, TX 77036 | Oil & Gas Operator | Dec 2001 |
| 442 | Wild Cat Operating Company | Victoria, TX 77903 | Oil & Gas Operator | Mar 2008 |
| 443 | Wood Energy Corporation | Baytown, TX 77520 | Oil & Gas Operator | Jun 1999 |
| 444 | Woodard Energy Company | Houston, TX 77042 | Oil & Gas Operator | Mar 2010 |
| 445 | Wright Brothers Energy, Inc. | Boerne, TX 78006 | Oil & Gas Operator | May 2025 |
| 446 | XTO Energy Inc. | Spring, TX 77389 | Oil & Gas Operator | May 2025 |
| 447 | Yuma E & P Company, Inc. | Houston, TX 77027 | Oil & Gas Operator | May 2025 |
| 448 | Zachry Exploration, LLC | San Antonio, TX 78224 | Oil & Gas Operator | May 2025 |