California ISO (CAISO)

The California Independent System Operator (CAISO) is a regional transmission organization (RTO) that manages the flow of electricity across the high-voltage, long-distance power lines for the grid serving 80 percent of California and a small part of Nevada. CAISO also administers the Western Energy Imbalance Market (EIM), which is a voluntary real-time wholesale energy trading market that allows participants across the Western grid to buy and sell real-time energy. 

CAISO administers access to the transmission grid in its market area, facilitates day-ahead and real-time energy markets, operates the bulk electric grid to ensure reliability, and conducts an annual transmission planning process. CAISO was created in 1998 because of California state legislation (AB 1890), which deregulated the state’s electric industry. Subsequently, CAISO was incorporated as a nonprofit public benefit corporation.

Map of system operators in California and Western Nevada showing the CAISO region


Map of the Western Energy Imbalance Market administered by CAISO