The transmission grids are operated by transmission system operators (TSOs), not-for profit companies that are typically owned by the utilities in their respective service areas, where they coordinate, control and monitor the operation of the electrical power system. TSOs are obliged to provide nondiscriminatory transmission access to electricity generators and customers. TSOs can be of two types: Independent System Operators (ISOs) and Regional Transmission Organizations (RTOs). The former operate within a single state, and the latter cover wider areas crossing state borders.
In 2009 there were four RTOs in the U.S.:
ISO New England (ISO-NE, which is an RTO despite its name);
Midcontinent Independent System Operator;
PJM Interconnection in the Mid-Atlantic region; and
Southwest Power Pool (SPP) covering Oklahoma, Kansas and parts of Arkansas, Missouri, Texas and New Mexico.
There are also three ISOs:
California Independent System Operator (California ISO);
New York Independent System Operator (NYISO);
Electric Reliability Council of Texas (ERCOT, an ISO).
https://en.wikipedia.org/wiki/North_American_power_transmission_grid
We’ve always known that.