| 501 | Dunbar, Ron, Inc. | Longview, TX 75606 | Oil & Gas Operator | Jan 2012 |
| 502 | Duncan Drilling Co. | Big Spring, TX 79721 | Oil & Gas Operator | Apr 2026 |
| 503 | Duncan Energy Company | Denver, CO 80202 | Oil & Gas Operator | Mar 2008 |
| 504 | Duncan Energy LLC | Dallas, TX 75231 | Oil & Gas Operator | Apr 2026 |
| 505 | Duncan Land & Exploration, Inc. | Graham, TX 76450 | Oil & Gas Operator | Apr 2026 |
| 506 | Duncan Oil Company | Holliday, TX 76366 | Oil Operator | Mar 2008 |
| 507 | Duncan Oil Inc | Denver, CO 80210 | Oil & Gas Operator | Jun 2016 |
| 508 | Duncan Oil Properties, Inc. | Oklahoma City, OK 73102 | Oil & Gas Operator | Apr 2026 |
| 509 | Dundee Oil & Supply Inc | Tulsa, OK 74101 | Oil & Gas Operator | Apr 2001 |
| 510 | Dundee Petroleum, Inc. | Buffalo Gap, TX 79508 | Oil & Gas Operator | Aug 2003 |
| 511 | Dune Oil And Gas, Inc. | Odessa, TX 79768 | Oil & Gas Operator | Aug 2006 |
| 512 | Dune Operating Company | Dallas, TX 75201 | Oil & Gas Operator | Jun 2016 |
| 513 | Dune Petroleum Corporation | Midland, TX 79702 | Oil & Gas Operator | Apr 1997 |
| 514 | Dunigan Operating Company, Inc. | Austin, TX 78755 | Oil & Gas Operator | Apr 2026 |
| 515 | Dunigan Petroleum, Inc. | Dallas, TX 75201 | Oil & Gas Operator | Aug 2003 |
| 516 | Dunlap Exploration, Inc. | Fort Worth, TX 76101 | Oil & Gas Operator | Nov 2016 |
| 517 | Dunlap, Rodge | Olney, TX 76374 | Oil & Gas Operator | Aug 2002 |
| 518 | Dunn Resources, LLC | Shreveport, LA 71115 | Oil & Gas Operator | Mar 2023 |
| 519 | Dunne Equities Operating, Inc. | Houston, TX 77057 | Oil & Gas Operator | Aug 2022 |
| 520 | Dunne Equities, Inc. | Wichita, KS 67226 | Oil & Gas Operator | Apr 2014 |
| 521 | Duplantis Energy, LLC | Pleasanton, TX 78064 | Oil Operator | Apr 2026 |
| 522 | Durango Operating Co., Inc. | Abilene, TX 79604 | Oil & Gas Operator | Feb 2002 |
| 523 | Durango Resources Corp. | Houston, TX 77043 | Oil & Gas Operator | Apr 2026 |
| 524 | Durham, Inc. | Midland, TX 79701 | Oil & Gas Operator | Jul 2016 |
| 525 | Durst Oil Company | Corpus Chrsti, TX 78477 | Oil & Gas Operator | Sep 2000 |
| 526 | Duster Production, Inc. | Refugio, TX 78377 | Oil & Gas Operator | Oct 2011 |
| 527 | Duval Gas Gathering Corporation | Austin, TX 78711 | Oil & Gas Operator | Apr 2026 |
| 528 | DWP Oil & Gas | Wichita Falls, TX 76309 | Oil & Gas Operator | Apr 2026 |
| 529 | DWR Oil Company | Merkel, TX 79536 | Oil & Gas Operator | Aug 2025 |
| 530 | Dyad Petroleum Company | Midland, TX 79710 | Oil & Gas Operator | Sep 2021 |
| 531 | Dyersdale Energy, L.P. | Kilgore, TX 75663 | Oil & Gas Operator | Apr 2026 |
| 532 | Dyersdale Production Co, Inc. | Houston, TX 77019 | Oil & Gas Operator | Apr 2026 |
| 533 | Dym Energy, Inc. | Celina, TX 75009 | Oil & Gas Operator | Apr 2018 |
| 534 | Dynamic Offshore Res. NS, LLC | Houston, TX 77010 | Oil & Gas Operator | May 2010 |
| 535 | Dynamic Offshore Resources, LLC | Houston, TX 77042 | Oil & Gas Operator | Apr 2026 |
| 536 | Dynamic Petroleum Res., Inc. | Houston, TX 77068 | Oil & Gas Operator | Jul 1994 |
| 537 | Dynamic Production, Inc. | Fort Worth, TX 76102 | Oil & Gas Operator | Apr 2026 |
| 538 | Dyne Oil & Gas,Inc. | Borger, TX 79008 | Oil & Gas Operator | Dec 2017 |
| 539 | Dyson Energy Operating, LLC | Bryan, TX 77802 | Oil & Gas Operator | Jun 2018 |