Regional Market Participation Rates in the Southeast

Competitive Wholesale Market

• Independent System Operator (ISO): “An independent, federally regulated entity established to coordinate regional transmission in a non-discriminatory manner and ensure the safety and reliability of the electric system.” (Source: EIA)
• Regional Transmission Organization (RTO): “A voluntary organization of electric transmission owners, transmission users and other entities approved by the Commission to efficiently coordinate electric transmission planning (and expansion), operation and use on a regional (and interregional) basis. Operation of transmission facilities by the RTO must be performed on a non-discriminatory basis.” (Source: FERC)

Examples:

• PJM Interconnection (PJM)
  • A regional transmission organization across the Mid-Atlantic and parts of the Midwest
• Southwest Power Pool (SPP)
  • SPP covers the Great Plains and the Midcontinent and is in the process of expanding further to the Western US;
• Midwest Independent System Operator (MISO)
  • MISO spans the Upper Midwest and parts of the Southern US

Utility-Organized Market

• Bilateral trading - "A direct contract between a seller and buyer outside of a centralized market or exchange. In energy markets, the buyer or seller usually finds his or her matching counter-party through a broker." (Source: FERC Glossary)
  • Example: Southeastern Energy Market (SEEM)
    • “The SEEM platform facilitates sub-hourly, bilateral trading, allowing participants to buy and sell power close to the time the energy is consumed, utilizing available unreserved transmission. Participation in SEEM is open to other entities that meet the appropriate requirements.” (Source: SEEM)

There has been a lack of easily accessible, open state-level customer count data available neither from these entities nor in aggregate, limiting the ability to conduct state-level assessments and evaluations (e.g., state-level savings per customer). Below, we briefly describe our methodological approach to estimate customer participation in regional markets.

Measuring Regional Market Participation: We used geographical data on electric retail service territories from Oak Ridge National Laboratory (ORNL) to identify utilities located in each market (MISO, PJM, SPP) and combined it with U.S. Energy Information Administration (EIA) customer data to uncover wholesale market participation.² These values are best approximations across multiple data sources as of December 2022, the release date of the latest publicly available ORNL data.

Because some utility territories cross state lines, it is difficult to cleanly separate which customers within a given state are served by RTO-participating utilities versus non-participating ones. While EIA Form 861 publishes state-level customer count data annually, the ORNL territorial data has not been updated since December 2022. This limits the ability to replicate RTO/ISO customer count estimates by state moving forward.

SEEM Participation: Evaluating SEEM is useful, as it represents a degree of regional coordination to facilitate energy transactions across the Southeast. However, because SEEM is organized at the utility level rather than the state level, trading volume data are likewise available at the same resolution, and detailed state-level participation data are limited. Additionally, SEEM's trading volumes only represent approximately 1% of total bilateral trading in the region (Tsoukalis et al. 2026). A granular, continuous measure of participation intensity would therefore convey little meaningful variation across states.

For these reasons, we use a binary indicator of SEEM involvement rather than a continuous measure of participation intensity. Readers seeking additional details on trading volume can assess SEEM’s annual reports (Potomac Economics 2025, SEEM n.d.).

Full methodological details are available in the Power Sector Competitiveness Dashboard Methodology: Market Participation (p. 23).