Quick answer
With several nuclear reactors offline for rebuilds and demand rising, Ontario has relied more on gas plants. Gas and other sources grew from 6% of transmission-connected output in 2018 to 16.6% of the supply mix in 2025.12
The shift
| Source | 2018 | 2025 |
|---|---|---|
| Nuclear | 61% | 48.5% |
| Natural gas, oil and other | 6% | 16.6% |
2018 figures are the IESO's transmission-connected generator output; 2025 figures are the system-wide supply mix, so they're not measured identically.12
Why gas filled the gap
OPG's CEO said in 2019 that gas assets become more important to the system when multiple nuclear units are being worked on, and expected gas to become a bigger energy provider after 2024.1
The path to 2050
The IESO's 2026 outlook plans for near-zero electricity emissions by 2050 by limiting gas production, while noting that meeting near-term energy needs could mean higher gas use depending on new supply.3
Common follow-up questions
Does more gas generation affect electricity prices?
Gas plants are often used in the busiest hours, so natural gas prices can influence the cost of power at peak times.
Is the extra gas use permanent?
Ontario's plans aim to reduce it as refurbished and new nuclear and other supply come online.
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Answers are general information as reported by the sources listed on the date shown, not personal financial or technical advice. Programs, prices and rules change. Canadian Energy Standard is an independent company, not affiliated with any government, utility or program named here.
- Financial Post, OPG's gas-plant purchases partly prompted by shifting nuclear landscape (August 2019)
- Ontario Energy Board, Ontario's system-wide electricity supply mix: 2025 data
- IESO, 2026 Annual Planning Outlook (March 2026)