Ancillary Services Scarcity Events on 5/4/25, 5/6/25 and 5/8/25

The California ISO has an ancillary services scarcity pricing mechanism in place that is triggered when the ISO is unable to procure the target quantity of one or more ancillary services in the integrated forward market or real-time market runs.

From May 4 to 8, 2025, ancillary service scarcity occurred in the 15-minute market run for the following regions, services and quantities:

Trade Date	Hour Ending	Interval	Ancillary Service	Region	Shortfall (MW)	Percentage of Requirement
May 4	10	1	Regulation Down	NP26_EXP	28.23	4.5%
May 4	11	4	Regulation Down	NP26_EXP	4.5	0.8%
May 6	9	4	Regulation Down	NP26_EXP	2.03	0.36%
May 8	17	4	Regulation Down	NP26_EXP	10.12	2.17%

The ISO confirmed the scarcity event during its price correction process. The published ancillary services prices correctly reflect the approved administrative set of scarcity prices.

Contact information

Please contact Jennie Araj at 916-351-2165 or jaraj@caiso.com with any questions.