| City Of Winona | Owner/operator | | | |
| City Public Service Board | Owner/operator | | | 1 |
| City Public Service Board Of San Antonio | Owner/operator | | | |
| City Water And Light Plant | Owner/operator | Jonesboro, AR | | 1 |
| City of Clarksville, Tennessee | Owner/operator | | 1 | |
| City of Duluth Public Works & Utilities | Owner/operator | Duluth, MN | 1 | 1 |
| City of LaGrange | Owner/operator | Lagrange, GA | 1 | 1 |
| City of Monroe | Owner/operator | | 1 | |
| Civil & Environmental Consultants, Inc. | Contractor | | 1 | |
| Civitas Permian Operating, LLC | Owner/operator | | | 1 |
| Claiborne Natural Gas Inc | Owner/operator | | | |
| Clarke - Mobile Counties Gas Dist | Owner/operator | Jackson, AL | | 1 |
| Clarke - Mobile Counties Gas District | Owner/operator | Jackson, AL | | 1 |
| Clarko Contractors,inc | Owner/operator | | | |
| Clarksdale Public Utilities | Owner/operator | | | |
| Clarksville Gas & Water Dept | Owner/operator | | | |
| Clausen-Koch | Owner/operator | | | |
| Clausen-Koch Apc | Owner/operator | | | |
| Clausen-Koch Midwest United | Owner/operator | | | |
| Cle Intrastate Pipeline Inc | Owner/operator | Pineville, LA | | 1 |
| Clean Energy Texas LNG | Owner/operator | Willis, TX | | 1 |
| Clean Harbors Lone Mountain Facility | Owner/operator | Norwell, MA | | 1 |
| Clear Creek Storage Company, LLC | Owner/operator | Houston, TX | | 1 |
| Clearfield Municipal Gas System | Owner/operator | Lenox, IA | | 1 |
| Clearwater Pipeline Company LLC | Owner/operator | Oklahoma City, OK | | 1 |
| Cleco Corporate Holdings, LLC | Owner/operator | | 1 | |
| Cleco Corporation | Owner/operator | | 1 | |
| Cleco Power LLC | Owner/operator | Pineville, LA | 2 | 1 |
| Cleveland-Cliffs Steel Corporation | Owner/operator | Cleveland, OH | | 1 |
| Clifty Group, LLC | Contractor | | | |
| Clinton - Newberry Natural Gas Auth | Owner/operator | Clinton, SC | | 1 |
| Clover Production Company | Owner/operator | Sour Lake, TX | | 1 |
| Coal Gas Recovery Ii, LLC | Owner/operator | Waynesburg, PA | | |
| Coalfield Pipeline Co | Owner/operator | Lexington, KY | | 1 |
| Coastal Bend LNG Development LLC | Owner/operator | | 1 | |
| Coastal Caverns, Inc. | Owner/operator | Houston, TX | | 1 |
| Coastal Eagle Point Oil Co | Owner/operator | | | |
| Coastal States Tradi | Owner/operator | | 1 | |
| Coastland Operations LLC | Owner/operator | Dallas, TX | | 7 |
| Coaxis Capital, LLC | Owner/operator | Sioux Falls, SD | | |
| Cobra Oil & Gas Corp. | Owner/operator | Wichita Falls, TX | | 1 |
| Cobra Operating Company | Owner/operator | | | |
| Cobra Pipeline Company, Ltd. | Owner/operator | Mentor, OH | | 1 |
| Coffeyville Resources Crude Transportation, LLC | Owner/operator | Sugar Land, TX | | 1 |
| Coffeyville Resources Refining And Marketing, LLC | Owner/operator | Coffeyville, KS | | 1 |
| Cog Operating LLC | Owner/operator | | | 1 |
| Cogar Right Of Way Clearing, LLC | Contractor | Webster Springs, WV | 1 | |
| Cogent Intrastate Pipeline,llc | Owner/operator | | | |
| Cogent Midstream | Owner/operator | | 1 | |
| Cogent Midstream Logistics, LLC | Owner/operator | | | |