| 601 | Cummings Oil & Cattle | Ada, OK 74820-0994 | Oil Operator | Jan 2017 |
| 602 | Cummings Oil Company | Oklahoma City, OK 73112-6113 | Oil & Gas Operator | Oct 2024 |
| 603 | Cummins Wren Oil Company | Tulsa, OK 74135 | Oil & Gas Operator | Nov 1998 |
| 604 | Cundiff Harold | Perkins, OK 74059-4199 | Oil & Gas Operator | Oct 2024 |
| 605 | Cundiff Jack | Perkins, OK 74059-4198 | Oil & Gas Operator | Apr 2014 |
| 606 | Curn Lisa | Steubenville, OH 43952-2535 | Oil Operator | Aug 2024 |
| 607 | Curran Oil Co | Great Falls, MT 59401 | Gas Operator | May 2001 |
| 608 | Curzon Operating Company LTD | Oklahoma City, OK 73118-4821 | Oil & Gas Operator | Sep 2024 |
| 609 | CVR Supply & Trading LLC | Sugar Land, TX 77479 | Oil & Gas Operator | Apr 2024 |
| 610 | CW Investments | Okmulgee, OK 74447-4026 | Oil & Gas Operator | Oct 2024 |
| 611 | CWB Energy Inc | Oklahoma City, OK 73139-8837 | Oil Operator | May 2000 |
| 612 | CX Disposals LLC | Minco, OK 73059-9472 | Oil Operator | Sep 2024 |
| 613 | Cxy Energy, Inc. | Dallas, TX 75251 | Oil & Gas Operator | Nov 2000 |
| 614 | Cyanostar Energy, Inc | Tulsa, OK 74103-4122 | Oil & Gas Operator | Sep 2001 |
| 615 | Cypress Exploration Company | Tulsa, OK 74132 | Oil & Gas Operator | Oct 2024 |
| 616 | Czar Resources Inc | Houston, TX 77060 | Oil & Gas Operator | Oct 1992 |