Summer Vs. Winter Blend Gas: What’s The Difference And Why It Matters

Why Seasonal Gas Blends Exist

Gasoline is a mixture of hydrocarbons, and some of those evaporate more easily than others. When temperatures rise, so does the rate of evaporation, which can lead to increased emissions and smog. To combat this, the EPA mandates specific Reid Vapor Pressure (RVP) levels for gasoline depending on the season and geographic region.

• Reid Vapor Pressure (RVP) measures how easily fuel evaporates.

• Lower RVP means less evaporation = better for warm weather.

• Higher RVP allows easier starting in cold weather.

Summer Blend Gasoline

Summer blend gas is used from June 1 through September 15 (or earlier in some areas).

Key Features:

• Lower RVP to reduce emissions and smog.

• Contains more additives to boost performance in higher temps.

• More expensive to produce, which can raise pump prices.

• Burns cleaner, making it better for air quality during hot months.

Pros:

• Environmentally friendlier

• Reduces evaporative emissions

• Keeps air cleaner in urban areas

Cons:

• Higher cost

• May slightly reduce mileage due to denser formulation

Winter Blend Gasoline

Winter blend gas is used from September 16 through May 31 (again, varying by region).

Key Features:

• Higher RVP to make cold-starts easier in freezing temps.

• Contains lighter hydrocarbons like butane, which vaporize more easily.

• Cheaper to produce, often reflected in lower gas prices during winter.

Pros:

• Helps your engine start in cold weather

• Typically costs less per gallon

Cons:

• Evaporates more easily, which increases pollution in warm temps

• Can lead to higher emissions if used improperly in warmer conditions

Why It Matters for You

You don’t need to choose which blend you get—it’s done automatically by suppliers—but knowing the difference can help explain:

• Why gas prices go up in summer

• Why your fuel economy may shift slightly with the seasons

• Why emissions rules change depending on location

If you’re storing gas (like in a mower or emergency supply), note that summer blend has a longer shelf life due to lower volatility.

The Bottom Line

The switch between summer and winter gas blends is a behind-the-scenes adjustment that keeps your car running smoothly and helps protect the environment. It’s another example of how small seasonal changes—like the fuel in your tank—can make a big impact.