| 601 | Crystal Energy Inc | Oklahoma City, OK 73116 | Oil & Gas Operator | Feb 2019 |
| 602 | Csoda Operating Company LLC | Amarillo, TX 79114-7506 | Oil & Gas Operator | Aug 2021 |
| 603 | CSX Oil & Gas Corporation | Houston, TX 77210-4326 | Oil & Gas Operator | Mar 1993 |
| 604 | Cudd Operating Corp. | Oklahoma City, OK 73118 | Oil & Gas Operator | Apr 2020 |
| 605 | Cuesta Petroleum Inc | Shawnee, OK 74801-6963 | Oil & Gas Operator | Dec 2024 |
| 606 | Culbreath Oil & Gas Co Inc | Tulsa, OK 74135 | Oil & Gas Operator | Dec 2024 |
| 607 | Culebra Oil & Gas, LLC | Kerrville, TX 78028 | Oil & Gas Operator | Apr 2025 |
| 608 | Culp & Copple Oil Company | Cushing, OK 74023 | Oil & Gas Operator | Apr 2022 |
| 609 | Cumberland Operating Company | Seminole, OK 74868-1258 | Oil & Gas Operator | Mar 2007 |
| 610 | Cummings Gene | | Oil Operator | Dec 2000 |
| 611 | Cummings Oil & Cattle | Ada, OK 74820-0994 | Oil Operator | Jan 2017 |
| 612 | Cummings Oil Company | Oklahoma City, OK 73112-6113 | Oil & Gas Operator | Jan 2025 |
| 613 | Cummins Wren Oil Company | Tulsa, OK 74135 | Oil & Gas Operator | Nov 1998 |
| 614 | Cundiff Harold | Perkins, OK 74059-4199 | Oil & Gas Operator | Jan 2025 |
| 615 | Cundiff Jack | Perkins, OK 74059-4198 | Oil & Gas Operator | Apr 2014 |
| 616 | Curn Lisa | Steubenville, OH 43952-2535 | Oil Operator | Dec 2024 |
| 617 | Curran Oil Co | Great Falls, MT 59401 | Gas Operator | May 2001 |
| 618 | Curzon Operating Company LTD | Oklahoma City, OK 73118-4821 | Oil & Gas Operator | Dec 2024 |
| 619 | CVR Supply & Trading LLC | Sugar Land, TX 77479 | Oil & Gas Operator | Apr 2024 |
| 620 | CW Investments | Okmulgee, OK 74447-4026 | Oil & Gas Operator | Dec 2024 |
| 621 | CWB Energy Inc | Oklahoma City, OK 73139-8837 | Oil Operator | May 2000 |
| 622 | CX Disposals LLC | Minco, OK 73059-9472 | Oil Operator | Dec 2024 |
| 623 | Cxy Energy, Inc. | Dallas, TX 75251 | Oil & Gas Operator | Nov 2000 |
| 624 | Cyanostar Energy, Inc | Tulsa, OK 74103-4122 | Oil & Gas Operator | Sep 2001 |
| 625 | Cypress Exploration Company | Tulsa, OK 74132 | Oil & Gas Operator | Dec 2024 |
| 626 | Czar Resources Inc | Houston, TX 77060 | Oil & Gas Operator | Oct 1992 |