The Difference Between Winter- and Summer-Blend Gas

Summer-blend gas provides about 1.7 percent increased energy content, meaning it offers a slight boost in fuel economy. Here's how...

May 28, 2020

Summer has its benefits. Fishing season. Dirt-track racing. Wrenching in the garage with the door open and the tunes blaring. Add summer-blend gas to the list thanks to the slight fuel-economy boost it offers.

That’s because refiners alter their gasoline and diesel formulations depending on the seasons, and summer gasoline contains about 1.7 percent increased energy than winter-blend gas.

Regardless of the time of year, it pays to know a little about what’s going in your tank to ensure you’re properly maintaining your fuel system.

Under pressure

A primary difference between winter- and summer-blend gas is their Reid Vapor Pressure (RVP). RVP is a measure of how easily the fuel evaporates at increased temperatures.

The higher the fuel’s RVP, the more easily it evaporates.

Winter-blend fuel requires increased RVP. If the fuel doesn’t evaporate readily in cold temperatures, the engine will start hard and run rough when it’s cold outside.

To achieve this, refiners often blend winter gasoline with butane, a relatively inexpensive additive with a high RVP. They adjust the RVP of the final formulation to as high as 15.0 psi to help the gasoline ignite readily in the cold.

Filling car with gas

The law promotes summer-blend gas

Once the temperature warms up in summer, however, high-RVP gasoline can volatilize more easily, which contributes to increased emissions and air pollution.

For that reason, federal law restricts sales of gasoline with an RVP greater than 9.0 from June 1 through Sept. 15.

To comply, refiners reduce the amount of butane in the gasoline and instead use pricier additives, hence one reason gas prices generally increase in summer. The blending process also takes longer, adding to the cost.

Some areas set even lower RVP standards in summer to further limit emissions. California, for example, has a 7.0-psi limit. Given the state’s climate, refiners may sell summer-blend gas as early as April 1 and as late as Oct. 31.

For the most part, the semi-annual switch from winter- to summer-blend gas and vice versa happens seamlessly and goes unnoticed by drivers.

Solve diesel fuel injector problems with a good diesel fuel additive.

Lowest additive concentration

Whether it’s summer-blend gas or not, gasoline contains detergent additives designed to keep fuel injectors and other fuel-system components clean. This helps maximize your fuel economy and reduce emissions.

Some automakers, however, think the additive content, called the lowest additive concentration (LAC), is insufficient for modern vehicles.

It takes a low level of additive to pass the tests, and most gasoline on the market contains as little as 123 ppm of additive.

The low levels of detergent additives in modern gasoline allow deposits to build up on critical fuel-system components, and most motorists are unaware of how dirty the insides of their engines are.

Give your fuel system a deep clean

This is precisely why it’s a good idea to clean and maintain your fuel system with high-quality fuel additives, like those here.

Check out this post for a deep dive on whether fuel additives actually work.

P.i.® Performance Improver is a potent, one-tank additive that deep-cleans your fuel system.

Cleans fuel injectors, intake valves and combustion-chamber deposits
Reduces emissions and increases fuel economy up to 5.7 percent¹
Use every 4,000 miles


Upper Cylinder Lubricant preserves and builds upon those gains. It also provides vital lubrication to the upper part of the cylinders.

Lubricates upper cylinders to fight wear
Inhibits ethanol-related corrosion
Keeps injectors clean
Delivers 18 percent more lubricity than Lucas and 20 percent more than Sea Foam for better retention of horsepower and fuel economy

Upper cylinder lube
Diesel truck

We didn’t forget about you diesel burners. AMSOIL formulates a full line of potent additives that maximize power and fuel economy in diesels.

¹ Based on independent testing using EPA tests: Federal Test Procedure 75 (FTP), Supplemental Federal Test Procedure (US06), and the Highway Fuel Economy Test (HFET). Average fuel mileage increase of 2.3 percent.