The California ISO’s Western Energy Imbalance Market (EIM) is a real-time bulk power trading market, the first of its kind in the western United States. The Western EIM’s advanced market systems automatically find the lowest-cost energy to serve real-time customer demand across a wide geographic area. Utilities will maintain control over their assets and remain responsible for balancing requirements while sharing in the cost benefits the market produces for participants.

Since launching in 2014, the Western EIM has enhanced grid reliability and generated cost savings in the millions for its participants. Besides its economic advantages, the EIM improves the integration of renewable energy, which leads to a cleaner, greener grid.

EIM is governed by a five member body with delegated authority over rules specific to the Western EIM.



Balancing Authority of Northern California (Phase1) – entered 2019

Idaho Power Company – entered 2018

Powerex – entered 2018

Portland General Electric – entered 2017

Puget Sound – entered 2016

Arizona Public Service – entered 2016

NV Energy – entered 2015

PacifiCorp – entered 2014

California ISO – entered 2014


Salt River Project – entry 2020

Seattle City Light – entry 2020

Los Angeles Department of Water & Power – entry 2021

Public Service Company of New Mexico – entry 2021

NorthWestern Energy – entry 2021

Turlock Irrigation District – entry 2021

Balancing Authority of Northern California (Phase 2) – entry 2021

Avista – entry 2022

Tucson Electric Power – entry 2022

Tacoma Power – entry 2022

Bonneville Power Administration – entry 2022

Implementation documents

  • Tucson Electric Power
  • Tacoma Power
  • Avista
  • PacifiCorp
  • Bonneville Power Administration
  • NV Energy
  • Puget Sound Energy
  • Arizona Public Service
  • Portland General Electric
  • Idaho Power Company
  • Seattle City Light
  • Balancing Authority of Northern California
  • Salt River Project
  • Powerex Corp
  • Los Angeles Department of Water and Power
  • NorthWestern Energy
  • Public Service Company of New Mexico
  • Turlock Irrigation District

Active and pending participants