The Western Interconnection is currently facing unprecedented changes with the implementation of two new day-ahead market offerings – SPP’s Markets+ and CAISO’s Extended Day-Ahead Market (EDAM) – prompting necessary coordination for the West to remain reliable and efficient as the landscape of Western power markets evolve. Considering these changes, many parties are asking how multiple markets will work without a single ISO or Reliability Coordinator, and what mechanisms can limit the friction at market and reliability seams. SPP and Western market participants recently explored these questions and their implications at the Western Seams Symposium in Tempe, Arizona.
On February 26, 2026, SPP held the Western Seams Symposium, hosted by Salt River project (SRP), to discuss seams management opportunities and challenges through the lens of the Markets+ Day-Ahead Market and SPP’s RTO West expansion. The Symposium, attended by roughly 400 attendees both online and in person, highlighted participant perspectives on ‘getting it right’; how to best manage seams and bring the most value to the west. The event featured SPP staff and participant-led panel discussions and presentations, outlining how seams impact Western entities and regional operations, as well as how new and existing seams management mechanisms can be best utilized. With the development of Markets+ and EDAM, and the expansion of SPP with RTO West, seams are a growing focal point which has been highlighted by SPP’s collaboration with western stakeholders and other regional organizations to ensure effective seams management at Markets+ go-live. The event emphasized that Western seams are not a new challenge but represent current operational realities that require immediate and transparent policy coordination.
SPP brings a history of seams coordination experience from its Eastern RTO, where market-to-market agreements between SPP, MISO, and PJM have efficiently managed congestion and enabled economic transfers for over a decade. However, the symposium highlighted unique attributes that distinguish the West and East interconnections, presenting a fundamentally different challenge for market operators. Unlike Eastern RTOs that operate as single Balancing Authorities with functional control of transmission, Western markets will require coordination across 30+ distinct BAs that retain operational independence, as well as transmission owners, operators and generators established in the WECC. Contract path scheduling remains the dominant western power flow model operated outside CAISO,
while Markets+ and EDAM will use flow-based optimization—creating potential conflicts when market dispatch produces loop flows on paths managed under existing contract path assumptions. Unlike the East, which evolved into the current RTO/ISO structure over decades, the West will operate four day-ahead platforms simultaneously by late 2027: CAISO, Markets+, EDAM, and SPP RTO West. While the development of new market constructs in the west will by no means do away with seams, they do offer reliability coordination opportunities, enhanced operational transparency, and financial benefits for participants.
SPP Executive Vice President and COO Antoine Lucas framed the symposium around five guiding principles for seams management: prioritize reliability as the non-negotiable foundation upon which markets are built, increase market efficiency to capture cost savings and improve price signals across footprints, improve transparency to make inefficiencies visible and measurable, seek fairness and reciprocity particularly for transmission access and congestion revenue allocation, and balance independence and inclusivity so entities retain governance accountability while participating meaningfully in development processes. Lucas argued that multiple markets create redundancy and resilience rather than fragmentation, that market options create efficiency through accountability and transparency, and that independence and scale are not mutually exclusive when proper coordination frameworks exist.
SPP presented three specific coordination mechanisms currently in development and respective implementation timelines. The first is Inter-Market Optimization (IMO), a near-real-time framework enabling 5-minute economic transfers by sharing dispatch cost information between markets and iteratively optimizing power flows. Unlike Eastern market-to-market coordination—which manages congestion but doesn’t transfer energy – IMO would capture efficiency gains by moving power from lower-cost to higher-cost regions in real time, addressing the 20–40-minute E-tag scheduling lag that prevents real-time price convergence at market seams which can lead to dispatch inefficiencies. SPP targets 2028 deployment between Markets+ and RTO West, with potential expansion to EDAM, dependent on stakeholder design alignment in late 2026. The second mechanism is the Enhanced Curtailment Calculator (ECC), the Western equivalent of the Eastern Interchange Distribution Calculator (IDC), providing standardized, flow-based congestion management across System Operating Limits and Interconnection Reliability Operating Limits. The governing NAESB standard was approved in December 2025 after a three-year development process, and implementation through OATI is underway for 2026. ECC provides a foundational reliability and equity framework for congestion management regardless of market participation. Third, SPP announced the hiring of a Director of Seams Strategy, a recently created and dedicated role, which highlights SPP’s recognition that Western seams coordination requires sustained, specialized focus.
SPP outlined concrete implementation steps that will require cross-market engagement with CAISO and western stakeholders. During 2026, SPP will conduct a comparative review of EDAM and Markets+ market designs to identify alignment opportunities, develop a stakeholder governance structure specifically for cross-market seams discussions, advance IMO methodology development between RTO West and Markets+, and continue supporting ECC design and OATI implementation. Coinciding with Markets+ Wave 1 launch in October 2027, SPP will draft coordination agreements between market operators—potentially including a direct SPP-CAISO agreement—incorporating lessons from the first year of EDAM operations (launching in May 2026), and advance IMO Phase 2 design work. In 2028, along with Markets+ Wave 2 implementation, SPP is targeting operational deployment of IMO between Markets+ and RTO West. This will include refining coordination agreements based on at least one year of dual-market operational experience, and advancement of IMO Phase 2 planning – potentially extending to Markets+ and EDAM coordination. As SPP noted, “it takes two to have a party”. IMO development requires active CAISO and SPP engagement and alignment on common design principles, which has yet to be formally established.
In closing remarks, Carrie Simpson VP of Markets at SPP, synthesized the day’s themes signaling SPP’s broad commitment to seams coordination. Simpson expressed SPP’s intention to pursue future joint forums that include CAISO directly, recognizing that dialogue between market operators represents the critical next step for 2026. The symposium demonstrated the West’s readiness to take seams coordination seriously—with concrete technical frameworks including IMO and ECC, and outlined timelines through 2028. SPP’s proposals require active stakeholder and market operator engagement, as well as bilateral agreements for effective seams to become an operational reality. Effective and proactive management implementation at Markets+ go live requires that stakeholders remain actively engaged in seams design throughout the upcoming year.
CES’ Market IQ teams remains dedicated to serving market participants and stakeholders through direct consulting, and individual and monthly ISO/RTO reports, enabling you to stay on the cutting edge of North American power markets. For the full Western Symposium report which dives into the meeting in detail – request your copy today.
