| 501 | DCF Exploration | Lakewood, CO 80215 | Oil Operator | Dec 1989 |
| 502 | Dci Petroleum Inc | University Heights, OH 44118-3818 | Oil & Gas Operator | Dec 2017 |
| 503 | Dcor, L.L.C. | | Oil & Gas Operator | Jan 2026 |
| 504 | DCP Midstream, LLC | | Oil Operator | Jun 2016 |
| 505 | DCP Midstream, LP | Denver, CO 80237 | Oil Operator | Nov 2006 |
| 506 | DCP Operating Co LP | Houston, TX 77042 | Oil & Gas Operator | Nov 2025 |
| 507 | DCP, Inc. | | Oil & Gas Operator | Jun 1990 |
| 508 | DCS Energy | Throckmorton, TX 76483 | Oil Operator | Apr 2026 |
| 509 | DDC & T Operating Company, Inc | | Oil & Gas Operator | Jul 2005 |
| 510 | DDC Energy Corporation | Marietta, GA 30068 | Oil & Gas Operator | Mar 1997 |
| 511 | DDC Oil LLC | Rockwall, TX 75087-5383 | Oil Operator | Mar 2020 |
| 512 | DDC Production Company | Archer City, TX 76351 | Oil Operator | Apr 2026 |
| 513 | DDC Track, LLC | Bushland, TX 79012 | Oil Operator | Apr 2026 |
| 514 | DDD Exploration, Inc. | Amarillo, TX 79109 | Oil & Gas Operator | Apr 2026 |
| 515 | De & TZ LLC | Wellsville, KS 66092 | Oil Operator | Dec 2025 |
| 516 | De Central Operating, LLC | Fort Worth, TX 76107 | Oil & Gas Operator | Apr 2026 |
| 517 | De Compiegne Prop. Co. 20, The | Midland, TX 79702 | Oil Operator | Oct 2019 |
| 518 | De IV Operating, LLC | Midland, TX 79701 | Oil & Gas Operator | Apr 2025 |
| 519 | De Kalb Agric Assn Inc | Vernal, UT | Oil & Gas Operator | Jun 1965 |
| 520 | De La Torre Oil & Gas, Inc | McAllen, TX 78501 | Oil & Gas Operator | Apr 2026 |
| 521 | De Larios, R. V., LTD. | Wichita Falls, TX 76308 | Oil & Gas Operator | Apr 2026 |
| 522 | De LTD Family Partnership | Punxsutawney, PA 15767-2646 | Oil & Gas Operator | Dec 2022 |
| 523 | De Operating LLC | Austin, TX 78701 | Oil & Gas Operator | Apr 2017 |
| 524 | De Soto Oil & Gas, Inc. | | Oil & Gas Operator | Mar 2006 |
| 525 | De Soto Oil Properties, LLC | | Oil & Gas Operator | Jan 2026 |
| 526 | De V Operating, LLC | Fort Worth, TX 76107 | Oil & Gas Operator | Apr 2026 |
| 527 | De-Vac Inc. | Daisetta, TX 77533 | Oil Operator | Apr 2026 |
| 528 | De3 Operating LLC | Irving, TX 75038 | Oil & Gas Operator | Jun 2021 |
| 529 | Deacon, Thomas J. | Randolph, NY 14772 | Gas Operator | Dec 2024 |
| 530 | Dead Fern Resources Inc | Sperry, OK 74073 | Oil & Gas Operator | Feb 2026 |
| 531 | Dead Horse Oil & Gas LLC | Skiatook, OK 74070-9343 | Oil & Gas Operator | Jun 2015 |
| 532 | Deagen, Bill & Sons, LTD. | Stockdale, TX 78160 | Oil Operator | May 2018 |
| 533 | Dean Energy, Inc. | Midland, TX 79702 | Oil & Gas Operator | Nov 2019 |
| 534 | Dean Enterprises, Inc. | | Oil & Gas Operator | Jun 2019 |
| 535 | Dean Petroleum | | Oil & Gas Operator | Jun 2000 |
| 536 | Dean'S Well Servicing Inc | Ratliff City, OK 73481 | Oil & Gas Operator | Jan 2026 |
| 537 | Deanlake Operator, L.L.C. | Houston, TX 77010 | Oil & Gas Operator | Sep 2011 |
| 538 | Dearing, Inc. | Kilgore, TX 75663 | Oil & Gas Operator | Mar 2021 |
| 539 | Dearinger Compan | | Oil Operator | Dec 1994 |
| 540 | Debbie Carroll | | Oil & Gas Operator | Apr 1999 |
| 541 | Debeaux - Flores | | Oil & Gas Operator | Jan 2025 |
| 542 | Deblin Oil & Gas, Inc | | Oil & Gas Operator | Aug 1995 |
| 543 | Deblin Operating LTD | | Oil & Gas Operator | Jan 1997 |
| 544 | Debord Oil Producers | Lincoln, NE 68503 | Oil Operator | Dec 1998 |
| 545 | Debord Oil Producers Inc | | Oil Operator | Dec 2006 |
| 546 | Deca Energy Corporation | | Oil & Gas Operator | Aug 1986 |
| 547 | Decab Company | Victoria, KS 67671 | Oil Operator | Aug 1996 |
| 548 | Decalta International Corp | Denver, CO 80202 | Oil & Gas Operator | Mar 2015 |
| 549 | Dechant Oil Operations, LLC | Hutchinson, KS 67501 | Oil Operator | Dec 2025 |
| 550 | Deck Exploration Inc | Perry, OK 73077-0303 | Oil & Gas Operator | May 2013 |
| 551 | Deck Oil Company | Tulsa, OK 74101 | Oil & Gas Operator | Jun 2020 |
| 552 | Decker & Associates | | Oil & Gas Operator | Mar 1991 |
| 553 | Decker Lease Ope | | Oil Operator | Dec 1988 |
| 554 | Decker Operating Co., L.L.C. | Houston, TX 77008 | Oil & Gas Operator | Apr 2026 |
| 555 | Decker Petroleum | | Oil & Gas Operator | Oct 2002 |
| 556 | Decker Well Service LLC | Fleming, OH 45729 | Oil & Gas Operator | Dec 2017 |
| 557 | Decker, James K. & Tiffany J. | Jamestown, NY 14701 | Oil & Gas Operator | Dec 2024 |
| 558 | Declar Oil & Gas Inc | | Oil & Gas Operator | Dec 2012 |
| 559 | Decleva, Paul | Wichita Falls, TX 76302 | Oil & Gas Operator | Dec 2020 |
| 560 | Deco | Kilgore, TX 75662 | Oil & Gas Operator | Jan 1999 |
| 561 | Deco Oil Co. | | Oil Operator | Oct 2013 |
| 562 | Dedica Energy Corporation | Mattoon, IL 61938 | Oil & Gas Operator | Mar 2008 |
| 563 | Dee'S Oil | Wellington, TX 79095 | Oil & Gas Operator | Mar 2008 |
| 564 | Dee-Jay Exploration Company | Nichols Hill, OK 73116 | Oil & Gas Operator | Apr 2026 |
| 565 | Deem, J. F. Oil & Gas, LLC | Parkersburg, WV 26104 | Oil & Gas Operator | Dec 2021 |
| 566 | Deem, W. A. | Harrisville, WV 26362-7878 | Oil & Gas Operator | Dec 2001 |
| 567 | Deen Drilling Company | Archer City, TX 76351 | Oil & Gas Operator | Apr 2026 |
| 568 | Deep Creek Adventures, Co. | | Oil Operator | Dec 2018 |
| 569 | Deep Ford Gas Company | Charleston, WV 25321-0169 | Gas Operator | Dec 2021 |
| 570 | Deep Gully Oil LLC | Houston, TX 77292 | Oil Operator | Apr 2026 |
| 571 | Deep Hole Oil LLC | Ashland, KY 41105 | Oil & Gas Operator | Dec 2020 |
| 572 | Deep Reef Industries | Amarillo, TX 79101 | Oil & Gas Operator | Jan 2004 |
| 573 | Deep Resources LLC | Holmesville, OH 44633 | Oil & Gas Operator | Dec 2025 |
| 574 | Deep River Energy LLC | | Oil Operator | Dec 2025 |
| 575 | Deep Rock LLC | Tulsa, OK 74137-1612 | Gas Operator | Jun 2022 |
| 576 | Deep Rock Resources, Inc. | Dallas, TX 75206 | Oil & Gas Operator | Apr 2026 |
| 577 | Deep South Production | | Oil Operator | Dec 2023 |
| 578 | Deeprock Disposal Services, LLC | | Oil & Gas Operator | Sep 1991 |
| 579 | Deepwell Co | | Oil Operator | Jul 1989 |
| 580 | Deer Creek Inc | Cambridge, OH 43725 | Oil & Gas Operator | Dec 2019 |
| 581 | Deer Creek Oil & Gas | Atlanta, GA 30326-1000 | Gas Operator | Dec 1987 |
| 582 | Deer Oil & Gas | Marietta, OH 45750 | Oil & Gas Operator | Dec 2024 |
| 583 | Deer Run Oil & Gas LLC | Albion, PA 16401-8306 | Gas Operator | Dec 2025 |
| 584 | Deer Run Oil Lease, LLC | Caney, KS 67333 | Oil Operator | Dec 2025 |
| 585 | Dees Production LLC | | Oil Operator | Dec 2024 |
| 586 | Defranco Oil Account | Wichita Falls, TX 76307 | Oil & Gas Operator | Feb 2004 |
| 587 | Deg Energy, Inc. | Magnolia, TX 77354 | Oil & Gas Operator | Feb 2007 |
| 588 | Degaugh Well Service Inc | | Oil Operator | Jul 1989 |
| 589 | Degge Oil Field Service | Okemah, OK 74859-0269 | Oil Operator | Nov 2014 |
| 590 | Degge Oilfield Services LLC | Okemah, OK 74859 | Oil Operator | Dec 2025 |
| 591 | Degroot, Garry | South Dayton, NY 14138 | Gas Operator | Dec 2024 |
| 592 | Deguello Operating LLC | College Sta, TX 77840 | Oil & Gas Operator | Apr 2026 |
| 593 | Dehart Company (The) | Ardmore, OK 73402 | Oil & Gas Operator | Feb 2026 |
| 594 | Deisenroth M Craig | Tulsa, OK 74104-6511 | Oil & Gas Operator | Jan 2026 |
| 595 | Deitz Edith | Clarion, PA 16214-9416 | Oil & Gas Operator | Dec 2009 |
| 596 | Deitz Gas & Oil Inc | Clarion, PA 16214-3215 | Oil & Gas Operator | Dec 2024 |
| 597 | Dejong John B | | Oil Operator | Dec 2025 |
| 598 | Deka Exploration Inc | Oklahoma City, OK 73113-0057 | Oil & Gas Operator | Nov 2019 |
| 599 | Dekalb Energy Company | Oklahoma City, OK 73134 | Oil & Gas Operator | Oct 1996 |
| 600 | Dekasco, Inc. | | Oil & Gas Operator | May 1990 |