Reliability Outlook


Cover of Reliability Outlook

The quarterly Reliability Outlook (formerly known as the 18-Month Outlook) presents Ontario’s demand forecast and associated drivers, resource adequacy projections and the assumptions that inform them, as well as an assessment of operability and the province’s transmission assets.

In addition to the Reliability Outlook and associated data tables and methodology, the IESO has made its Transfer Capability Assessment Methodology for the Near-Term Transmission Planning Horizon publically available. The Ontario Transmission System document was consolidated with this Transfer Capability Assessment Methodology document. Operating Limits previously documented in the Ontario Transmission System document are now available in the Reliability Outlook Tables.

The IESO issues its Reliability Outlook each quarter. Here is the most recent issue and related documents.

From January 2024 to June 2025 

  • Methodology to Perform the Reliability Outlook contains information regarding the methodology used to perform the demand forecast, resource adequacy assessments, and transmission adequacy assessments in this Outlook report.
  • Transfer Capability Assessment Methodology documents the methodology used for performing assessments of Transfer Capability of the Ontario Bulk Electric System (BES) for transmission planning studies.  This methodology is in accordance with the North American Electric Reliability Corporation (NERC) standard FAC-013-2. The IESO has also utilized this methodology for the transmission assessment beyond the first 18 months in the Reliability Outlook.

Previous Reliability Outlook Reports and related information can be found in the Document Library, under the Planning and Forecasts category.

For Reliability Outlook Reports and related information prior to December 2020, please contact customer.relations@ieso.ca and specify the document, year and quarter requested, and advise whether it needs to be provided in an accessible format.


Submitting of Reliability Assessment Information

Market participants are required to provide information to the IESO to enable it to conduct reliability assessments. These submissions are required each calendar year.

For submission deadlines for input information for the Reliability Outlook and other reliability assessments, see the Calendar for Submission of Reliability Assessments Information.

Related Information

The IESO reports reserve margin requirements over a five-year window as required by the Ontario Resource and Transmission Assessment Criteria. Generally published in the Annual Planning Outlook, Ontario's 5-year reserve margin requirements for 2024 to 2028 can be found here.


Additional Planning and Forecasting documents, previously referenced on this page, can be obtained by contacting customer.relations@ieso.ca. These archived documents include: Ontario Reliability Outlook, Ontario Planning Outlook, 10-Year Outlook, Integrated Power System Plan, Long-Term Energy Plan and Supply Mix Advice. Please allow a minimum of one business day for a response and advise whether the document(s) need to be provided in an accessible format.