A deeper look at volatility, seasonal blending and why the gasoline at the pump changes with the weather.

Yes, summer and winter gasoline are different. Across Canada, gasoline formulations are adjusted through the year so fuel performs reliably as temperatures change while meeting fuel-quality and environmental requirements.

The key difference: volatility

Volatility is how readily gasoline turns from liquid into vapour. In cold weather, gasoline needs to vaporize readily enough to support reliable starting and operation. Winter gasoline is therefore formulated with higher volatility. In warm weather, excessive evaporation can increase emissions of volatile organic compounds (VOCs), which can contribute to ground-level ozone and smog. Summer gasoline is formulated to be less volatile.

What is RVP?

Reid Vapour Pressure (RVP) is a standard measure of gasoline volatility at 37.8°C (100°F). Higher RVP means the fuel vaporizes more readily; lower RVP means it is less volatile. Canadian fuel requirements recognize seasonal differences, and the federal Benzene in Gasoline framework uses different summer and winter parameters.

What changes inside the blend?

Gasoline is not one substance. It is a carefully balanced mixture of refinery blendstocks and other components. These can include naphthas, alkylate, isomerate, pentanes, butane and ethanol. Refiners adjust the recipe to achieve the required octane, volatility, emissions performance and other specifications.

Butane is a useful example. It is a relatively low-cost, high-octane component with high volatility. More butane can generally be blended into winter gasoline, where that volatility supports cold-weather performance. Its use is reduced in summer to help meet lower-volatility specifications. Ethanol also affects blend volatility, so refiners adjust the surrounding gasoline blend to ensure the finished fuel meets seasonal requirements.

Why can summer gasoline cost more to make?

Summer gasoline typically requires tighter volatility control, less use of lower-cost highly volatile components such as butane, and greater use of other blending components. The seasonal transition also adds manufacturing, inventory and logistics complexity. That can make summer gasoline more expensive to produce, although retail prices are influenced by many other factors—including crude oil prices, demand, inventories, transportation, taxes and local market conditions.

The bottom line

The fuel changes because the weather changes. Winter gasoline is formulated to vaporize more readily in cold conditions. Summer gasoline is formulated to evaporate less readily in warm conditions, helping control evaporative emissions. Drivers may barely notice the transition, but refiners and fuel suppliers plan for it every year.