Electricity is generated and sold in a New England-wide wholesale market. There are also sales into this market from New York and Canada. The New England market works under a series of rules and regulation approved by the Federal Energy Regulatory Commission (FERC) and administered by the New England Independent System Operator (NE ISO), the same organization charged with maintaining the reliability of the electric grid and keeping the lights on. There are numerous generators and other suppliers who generate or buy for resale all of the electricity that flows in New England. Some of this power is bought and sold under contracts, and some is sold into a "spot" market where the price is set by the highest bid.
The wholesale market is different in Northern Maine. There, the electric grid is not connected to the New England grid except by going through New Brunswick. This has led to a different market, dominated by New Brunswick Power. The organization responsible for reliability is the Northern Maine Independent System Administrator (NMISA).