2026 Integrated System Plan (ISP)

2025-26 Inputs, Assumptions and Scenarios

AEMO delivers a range of planning and forecasting publications to inform decision making including the Electricity Statement of Opportunities (ESOO), the Gas Statement of Opportunities (GSOO) and the Integrated System Plan (ISP).

AEMO strives to ensure its planning and forecasting publications are of highest quality, with data that is fit for purpose and industry-reviewed and processes that are transparent. To build confidence in the forecasts, and help decision makers understand the outcomes, AEMO consults on and publishes its scenarios, inputs, assumptions and methodologies. Confidential information is withheld from public release, but is incorporated in the modelling conducted, if necessary, to deliver assessments that are as accurate as possible.

2025 Inputs, Assumptions and Scenarios 

AEMO consulted on the Draft 2025 Inputs, Assumptions and Scenarios Report (IASR) between December 2024 and March 2025.

The following documents contain descriptions and details of the scenarios, and the associated inputs and assumptions currently applied in AEMO’s 2025-26 Forecasting and Planning activities.

Reports

2026 ISP Scenario weighting

Ahead of the Draft 2026 ISP release on 10 December 2025, AEMO has assessed the relative likelihood of key energy planning scenarios.

To support this, AEMO held a full-day deliberative workshop with 25 energy sector representatives in September 2025. Participants assessed the relative likelihood of 18 key parameters that underpin the scenarios through individual and anonymous voting, and group discussion. AEMO combined these insights with its own approach to reflect the relative importance of each parameter.

These scenario weightings will impact the selection of the 2026 ISP Optimal Development Path, with 'Step Change' identified as the most likely scenario.

2025 Electricity Network Options Report 

AEMO consulted on the Draft 2025 Draft 2025 Electricity Network Options Report between May and June 2025. This report identifies potential augmentation options in electricity networks within the National Electricity Market and considers both transmission and distribution opportunities.

Reports

2025 Gas Infrastructure Options Report 

AEMO consulted on the Draft 2025 Gas Infrastructure Options Report between May and June 2025. This new report outlines gas infrastructure options and gas infrastructure cost components to ensure that electricity investments – particularly in gas powered generation – consider and are resilient to the capacity, availability and limitations of gas as a fuel for electricity generation.

Reports

IASR reference materials

Electricity Network Options Report reference materials

AEMO has also released Version 3.1 of its Transmission Cost Database. Fill in this form to receive a copy and visit the Transmission Cost Database for more details.

Gas Infrastructure Options Report reference material

Other relevant input sources

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