​The Day-Ahead Ancillary Services (DA A/S market) launched in ISO New England on March 1, 2025. It replaced the Forward Reserve Market and co-optimizes day-ahead energy and ancillary services in a single daily clearing. Winter accounted for 60% of the first full-year total, but even that understates how concentrated the cost was.

Key takeaways

• Winter Storm Fern (Jan 25–29, 2026) contributed 40%, and single day (January 27, 2026) accounted for 18%.
• Combustion turbine outage rates fell from 18% to 11% after DA A/S launched which is the market's clearest reliability signal.
• ISO-NE has proposed various reforms, including a fuel-cost-based floor to the strike price, targeting Q4 2026 implementation.

TMNSR carried more than half the first-year pool.

DA A/S clears three reserve products day-ahead: ten-minute spinning reserve (TMSR), ten-minute non-spin reserve (TMNSR), and thirty-minute operating reserve (TMOR).

Across the full first year, TMNSR settled at $114 million (43%), TMSR at $74 million, TMOR at $60 million. Winter 2026 amplified the pattern when TMNSR cleared $65 million in one quarter alone.

Twelve days drove half the revenue, but high costs are making ISO-NE change market design.

The Internal Market Monitor (IMM) estimated that DA A/S increased total costs by $974 million in its first year versus the prior energy-only design, or roughly 9% ($8.23/MWh) of load served. That figure was far above ISO-NE's original 2023 impact assessment of $140 million per year.

About 75% of the gap from the original estimate is explained by changed market conditions:

• Natural gas prices doubled ($3→$7/MMBtu) and day-ahead Hub LMPs rose 113% from ($33→$71/MWh) versus the 2019-2021 reference period.

Within that elevated total, the distribution was extreme. Winter Storm Fern (January 25–29, 2026) contributed 40%, and January 27, 2026 alone accounted for 18%. Outside those twelve days, DA A/S costs tracked close to the IMM's competitive benchmark. Another proposed reform includes reducing the Pay-for-Performance cap (and associated penalty) from $9,337 to $3,500.

Combustion turbines dominated clearing and improved their availability.

• Oil-fired combustion turbines (CT) took 40–50% of cleared DA A/S MWh monthly
• Gas CTs added 10–20%
• Combined-cycle units led TMSR

Combustion turbine (CT) outage rates fell from an average 18% in the years before DA A/S to 11% after implementation. CTs now earn approximately $3.53/kW-month from DA A/S, compared with $1.30/kW-month under the prior Forward Reserve Market. DA A/S now represents roughly half of total CT revenue.

ISO-NE has proposed a fuel-cost floor that would reshape the ancillary services market

Due to the unexpected cost increases, ISO-NE has proposed adding a CT fuel-cost-based floor to the strike price, targeting Q4 2026 implementation.