On March 30, 2025, FERC approved revisions to Southwest Power Pool, Inc.’s (“SPP”) Open Access Transmission Tariff (“Tariff”) and Governing Documents to allow nine entities (“Expansion Members”) in the Western Interconnection to join SPP’s Regional Transmission Organization (“RTO”) as transmission-owning members (“RTO West”), on the condition that SPP submit compliance and informational filings. The approval makes SPP the first RTO to provide transmission and interconnection services across two of the three major interconnections, set to begin in April 2026.

On June 4, 2024, SPP filed its amended Tariff to accommodate the Expansion Members seeking to pursue RTO membership. In its filing, SPP explained that the Expansion Members’ Balancing Authority Areas (“BAA”) in the Western Interconnection are geographically contiguous with SPP’s existing footprint; however, the proposed expansion would span both the Eastern Interconnection and the Western Interconnection, with three direct current (“DC”) connections between the two. SPP’s proposed Tariff revisions distinguish between the SPP East Region and the SPP West Region. As proposed by SPP, SPP plans to operate two separate BAAs—a new Western BAA and its existing Eastern BAA—while leveraging the DC ties between them. SPP further explained that the Expansion Members would participate in SPP’s existing Integrated Marketplace, a centralized day-ahead and real-time energy and operating reserve market in the Eastern Connection, which will optimize the two BAAs to the maximum extent practicable using the DC ties.

SPP emphasized that its proposed Tariff revisions are primarily designed to accommodate the operation of a single market comprising two separate BAAs in different interconnections. However, the revisions contain only minimal alterations to SPP’s governance structure, market design, transmission services, generator interconnection procedures, cost allocation, and operational procedures. In support of the RTO West plan, SPP asserted that the expansion substantially expands the SPP footprint, which will provide significant benefits to both new and existing SPP members. SPP further provided that this expansion will provide access to organized markets for new members, thereby enhancing efficiency and reliability within the broader SPP footprint.

FERC determined that the RTO West tariff revisions were just and reasonable and agreed with SPP that the proposal to integrate Expansion Members in the Western Interconnection into the SPP RTO will likely enhance grid reliability and operational efficiency, to the benefit of both existing SPP members and the Expansion Members. FERC explained that RTO West will consolidate the management of transmission facilities under a single, centrally cleared market, allowing SPP to dispatch resources more efficiently across a broader geographic area. However, FERC also acknowledged that it did not yet have sufficient information to fully address all potential problems that could arise under the RTO West plan. For example, the order does not address seams issues raised by some intervenors or how the expanded RTO will interact with neighboring markets. Lastly, FERC directed SPP to submit a compliance filing within 30 days from the order and to submit an informational filing notifying the Commission of the effective date of its Tariff revisions no later than six months prior to the date SPP implements the proposed revisions.

FERC’s Order, issued in Docket No. ER24-2184, can be accessed here.