| Company | Parent Company | Sector | Type |
| A&C Management Group, LLC* | Not applicable | | Emergency Load Program Member |
| A123 Systems, Inc. | Not applicable | | Associate Membership |
| AC Energy, LLC | Not applicable | Other Supplier | Voting Member |
| Acciona Energy North America Corporation (AENAC) | Not applicable | Generation Owner | Voting Member |
| Achieving Equilibrium LLC | Not applicable | Other Supplier | Voting Member |
| AEP Appalachian Transmission Company, Inc. | Appalachian Power Company | Transmission Owner | Affiliate |
| AEP Energy Partners, Inc. | Appalachian Power Company | Other Supplier | Affiliate |
| AEP Energy, Inc. | Appalachian Power Company | Other Supplier | Affiliate |
| AEP Indiana Michigan Transmission Company, Inc. | Appalachian Power Company | Transmission Owner | Affiliate |
| AEP Kentucky Transmission Company, Inc. | Appalachian Power Company | Transmission Owner | Affiliate |
| AEP Ohio Transmission Company, Inc. | Appalachian Power Company | Transmission Owner | Affiliate |
| AEP Retail Energy Partners, LLC | Appalachian Power Company | Other Supplier | Affiliate |
| AEP West Virginia Transmission Company, Inc. | Appalachian Power Company | Transmission Owner | Affiliate |
| AES Armenia Mountain Wind, LLC | Dayton Power & Light Company (The) | Generation Owner | Affiliate |
| AES Beaver Valley, LLC | Dayton Power & Light Company (The) | Generation Owner | Affiliate |
| AES Energy Storage, LLC | Dayton Power & Light Company (The) | Generation Owner | Affiliate |
| AES Laurel Mountain, LLC | Dayton Power & Light Company (The) | Generation Owner | Affiliate |
| Agway Energy Services, LLC | Not applicable | Other Supplier | Voting Member |
| Air Liquide Industrials U.S., L.P. | Not applicable | End User Customer | Voting Member |
| Air Products & Chemicals, Inc. | Not applicable | End User Customer | Voting Member |
| AK Steel Corporation | Not applicable | End User Customer | Voting Member |
| Alcoa Power Marketing, LLC | Not applicable | Other Supplier | Voting Member |
| Algonquin Energy Services, Inc. | Not applicable | Other Supplier | Voting Member |
| Allegheny Electric Cooperative, Inc. | Not applicable | Electric Distributor | Voting Member |
| Allegheny Energy Supply Company, L.L.C. | FirstEnergy Solutions Corp. | Transmission Owner | Affiliate |
| ALLETE, Inc. d/b/a Minnesota Power | Not applicable | Other Supplier | Voting Member |
| Alliant Energy Corporate Services, Inc. | Not applicable | Other Supplier | Voting Member |
| Alliant Energy Resources LLC | Alliant Energy Corporate Services, Inc. | Other Supplier | Affiliate |
| Alpha Gas and Electric, LLC | Not applicable | Other Supplier | Voting Member |
| Alphataraxia Palladium LLC | Not applicable | Other Supplier | Voting Member |
| Ambit Northeast, LLC | Not applicable | Other Supplier | Voting Member |
| Ameren Energy Marketing Company | Not applicable | Generation Owner | Voting Member |
| American Efficient, Inc. | Not applicable | Other Supplier | Voting Member |
| American Illuminating Company, LLC | ResCom Energy, LLC | Other Supplier | Affiliate |
| American Municipal Power, Inc. | Not applicable | Electric Distributor | Voting Member |
| American Power & Gas of Pennsylvania LLC | Not applicable | Other Supplier | Voting Member |
| American Power Partners, LLC | Not applicable | Other Supplier | Voting Member |
| American PowerNet Management, L.P. | Not applicable | End User Customer | Voting Member |
| American Transmission Company, LLC | Not applicable | | Associate Membership |
| American Transmission Systems, Inc. | FirstEnergy Solutions Corp. | Transmission Owner | Affiliate |
| Amerigreen Energy, Inc. | Not applicable | Other Supplier | Voting Member |
| Analytical Applications* | Not applicable | | Emergency Load Program Member |
| Anbaric Northeast Transmission Development Company, LLC | Not applicable | Other Supplier | Voting Member |
| AP Gas & Electric (IL), LLC | AP Gas and Electric (PA), LLC | Other Supplier | Affiliate |
| AP Gas & Electric (MD), LLC | AP Gas and Electric (PA), LLC | Other Supplier | Affiliate |
| AP Gas & Electric (NJ), LLC | AP Gas and Electric (PA), LLC | Other Supplier | Affiliate |
| AP Gas & Electric (OH), LLC | AP Gas and Electric (PA), LLC | Other Supplier | Affiliate |
| AP Gas and Electric (PA), LLC | Not applicable | Other Supplier | Voting Member |
| APN Starfirst, LP | American PowerNet Management, L.P. | End User Customer | Affiliate |
| Appalachian Power Company | Not applicable | Transmission Owner | Voting Member |
| Apple Group, LLC | Not applicable | Other Supplier | Voting Member |
| APX Power Markets Inc. | Not applicable | | Associate Membership |
| Aquenergy Systems Inc. | Not applicable | Generation Owner | Voting Member |
| ArcelorMittal USA LLC | Not applicable | End User Customer | Voting Member |
| ArcLight Energy Marketing, L.L.C. | Not applicable | Other Supplier | Voting Member |
| Aspen Merchant Energy, LP | Velocity American Energy Master I, L.P. | Other Supplier | Affiliate |
| Associated Electric Cooperative, Inc. | Not applicable | Other Supplier | Voting Member |
| Astral Energy LLC | Not applicable | Other Supplier | Voting Member |
| Atlantic City Electric Company | Potomac Electric Power Company | Electric Distributor | Affiliate |
| Atlantic Grid Operations A, LLC | Not applicable | Other Supplier | Voting Member |
| Automated Algorithms, LLC | Not applicable | Other Supplier | Voting Member |