| Oakley Fuels Inc terminal | Terminal | AR | Oakley Fuels Inc | |
| Oakmar terminal | Terminal | MO | Oakmar Terminal LLC | |
| Oaktown | Underground storage | Knox County, IN | Texas Gas Transmission, LLC | In service |
| Oasis Compressor Station | Compressor station | Roger Mills County, OK | ET Gathering & Processing, LLC | |
| Oasis East | Compressor station | Fayette County, TX | | |
| Oasis West | Compressor station | Fayette County, TX | | |
| Odessa Railport | Terminal | TX | | |
| Odessa Terminal | Terminal | TX | | |
| Odfjell Terminals Charleston Charleston | Terminal | SC | Odfjell Terminals Charleston LLC | |
| Oexco Enogex Booster Station | Compressor station | Oklahoma County, OK | Oklahoma Gas Gathering LLC | |
| Ohio Govt C Kutz CDP | Compressor station | NM | Hilcorp Energy Company | |
| Ohio Govt La Plata CDP | Compressor station | NM | Hilcorp Energy Company | |
| Oil City Compressor Station | Compressor station | Carter County, OK | ET Gathering & Processing, LLC | |
| Oil Springs | Underground storage | Carbon County, WY | Black Hills Energy | In service |
| Oiltanking Texas City Texas City terminal | Terminal | TX | Oiltanking Texas City LP | |
| Ojito Compressor Station | Compressor station | NM | Harvest Four Corners, LLC | |
| Okarche | Gas processing plant | Kingfisher County, OK | DCP Operating Company, LP | In service |
| Okarche Booster Station | Compressor station | Kingfisher County, OK | Enable Oklahoma Intrastate Transmission, LLC | |
| Okarche Compressor Station | Compressor station | Canadian County, OK | Markwest Oklahoma Gas Company, LLC | |
| Okeene Booster Station | Compressor station | Blaine County, OK | DCP Operating Company, LP | |
| Okeene Terminal | Terminal | OK | | |
| Okemah Compressor Station | Compressor station | Okfuskee County, OK | Petrolink Energy LLC | |
| Oklahoma City Plant | Gas processing plant | Oklahoma County, OK | Herbert Malarkey Roofing Company | |
| Oklahoma City Terminal | Terminal | OK | | |
| Oklahoma Polyethylene Foam Extrusion Plant | Gas processing plant | Canadian County, OK | Armacell LLC | |
| Old Ocean Gas Plant | Gas processing plant | Brazoria County, TX | Harvest Pipeline Company | In service |
| Oliver | Underground storage | Posey County, IN | Southern Indiana Gas & Electric Co | In service |
| Oliver Creek JT Plant | Gas processing plant | Shelby County, TX | | |
| Omega Gas Plant | Gas processing plant | Kingfisher County, OK | Markwest Oklahoma Gas Company, LLC | |
| Omega PTNRS III Columbus 1 terminal | Terminal | GA | Omega PTNRS III LLC | |
| Omega Partners III Hartford terminal | Terminal | IL | Omega Partners III LLC | |
| Omega Partners III Henderson terminal | Terminal | KY | Omega Partners III LLC | |
| Omega Partners III Jacksonville terminal | Terminal | FL | Omega Partners III LLC | |
| One Bull Compressor Station | Compressor station | Custer County, OK | ET Gathering & Processing, LLC | |
| One Horse Compressor Station | Compressor station | Custer County, OK | ET Gathering & Processing, LLC | |
| Oneok Field Services Cedar Lake Compressor Station | Compressor station | Canadian County, OK | Oneok Field Services Inc | |
| Oneok Field Services Cherokee Compressor Station | Compressor station | Garvin County, OK | Oneok Field Services Inc | |
| Oneok Field Services Cheyenne Compressor Station | Compressor station | Harper County, OK | Oneok Field Services Inc | |
| Oneok Field Services Cimarron Compressor Station | Compressor station | Blaine County, OK | Oneok Field Services Inc | |
| Oneok Field Services Cottonwood Compressor Station | Compressor station | Stephens County, OK | Oneok Field Services Inc | |
| Oneok Field Services Eakly Compressor Station | Compressor station | Caddo County, OK | Oneok Field Services Inc | |
| Oneok Field Services Greenfield Compressor Station | Compressor station | Blaine County, OK | Oneok Field Services Inc | |
| Oneok Field Services Watonga Compressor Station | Compressor station | Kingfisher County, OK | Oneok Field Services Inc | |
| Oneok Gas Transportation Rock Creek Compressor Station | Compressor station | Okmulgee County, OK | Oneok Gas Transportation, LLC | |
| Oneok Hydrocarbon Bushton Storage Facility terminal | Terminal | KS | Oneok Hydrocarbon LP | |
| Oneok Hydrocarbon Hutchinson terminal | Terminal | KS | Oneok Hydrocarbon LP | |
| Oneok Mont Belvieu Storage terminal | Terminal | TX | Oneok Hydrocarbon LP | |
| Oneok North System Clear Lake terminal | Terminal | IA | Oneok North System LLC | |
| Oneok North System Des Moines terminal | Terminal | IA | Oneok North System LLC | |
| Oneok North System Iowa City terminal | Terminal | IA | Oneok North System LLC | |