Because of the complexity of operating the Grid, there is a requirement for a controlling agency. The transmission system operator coordinates the dispatch of generating units to meet the expected demand of the system across the transmission grid. In the United States, these agencies are known as Independent System Operators (ISO) s and Regional Transmission Organizations (RTO) s. These organizations coordinate, control and monitor the electricity transmission grid. If there is a mismatch between supply and demand, the generators speed up or slow down causing the system frequency to increase or decrease. If the frequency falls outside a predetermined range the system operator will act to add or remove either generation or load. RTOs typically perform the same functions as ISOs, but cover a larger geographic area. While each ISO operates and oversees its own region, there are often calls to dispatch power to neighboring grids. The cooperation between grid operators is essential to maintaining reliable supply and pricing.


Transmission Zones (sometimes referred to as The Grid) are run on regional and national levels by non-profit regulators who monitor demand and dictate generation. This complex process requires detailed forecasting and planning as well as moment by moment routing and adjusting of power generation to meet constantly fluctuating demands. The grid operators also oversee and monitor the purchase and sale of electricity on a wholesale level, which ensures reliable operation of the entire system.


An Independent System Operator (ISO) is an organization formed at the direction of the Federal Energy Regulatory Commission (FERC). In the areas where an ISO is established, it coordinates, controls, and monitors the operation of the electrical power system, usually within a single US State, but sometimes encompassing multiple states.


A regional transmission organization (RTO) is an organization responsible for moving electricity over large interstate areas. The RTO coordinates controls and monitors an electricity transmission grid that is larger with much higher voltages than a typical utility’s distribution grid. RTOs typically perform the same functions as ISOs, but cover a larger geographic area.

New England (ISO-NE)

ISO-NE oversees Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont

The marginal fuel type in New England is natural gas.

New York (NYISO)

NYISO oversees New York State

New York’s marginal fuel type is natural gas.

Mid-Atlantic (PJM)

PJM oversees all or most of Delaware, District of Columbia, Maryland, New Jersey, Ohio, Pennsylvania, Virginia and West Virginia and parts of Indiana, Illinois, Kentucky, Michigan, North Carolina and Tennessee.

The marginal fuel sources in the Mid-Atlantic are coal and natural gas.

Midwest (MISO)

MISO oversees all or most of North Dakota, South Dakota, Nebraska, Minnesota, Iowa, Wisconsin, Illinois, Indiana, Michigan and parts of Montana, Missouri, Kentucky, and Ohio.

Marginal fuel source for the Midwest is coal.

California (CAISO)

CAISO oversees most of California.

Marginal fuel source for California is natural gas.

Northwest (NWPP)

NWPP oversees all or most of Washington, Oregon, Idaho, Utah, Nevada, Montana, Wyoming and part of California.

Marginal fuel sources for NWPP are hydro and natural gas.

Southeast (SERC)

SERC oversees all or most of Florida, Arkansas, Louisiana, Mississippi, Alabama, Georgia, Tennessee, North Carolina, South Carolina and parts of Missouri, Kentucky and Texas

Marginal fuel sources for SERC are coal and natural gas

Southwest (WECC)

WECC oversees all or most of Arizona, New Mexico, Colorado and parts of Nevada, Wyoming and South Dakota.

Marginal fuel source for WECC is natural gas

Texas (ERCOT)

ERCOT oversees most of Texas

Marginal fuel sources for ERCOT are coal and natural gas