The Difference Between Summer and Winter Blend Gasoline

Throughout most parts of the United States, fuel stations switch to a summer blend of gasoline around the middle of May to the beginning of June. A routine New York City oil and gas inspection is done around this time in order to ensure that the pumps are delivering the right blend of fuel. Inspectors may also collect fuel samples to verify that the blend is correct. It is important to understand why the available fuel blends change and what the difference is between them.

The Purpose of Different Gasoline Blends

Across the United States, there are more than 20 gasoline blends in use. There are so many because of the different state and federal guidelines on air quality. Volatile organic compounds are released at a faster rate during hotter weather, so summer blends have to contain fewer of them in order to adhere to state and federal clean air requirements.

Reid Vapor Pressure

Gasoline blends are measured on a scale called the Reid Vapor Pressure Measurement. This measurement goes up to 14.7 pounds per square inch, which is the average atmospheric pressure across the USA. If a gas reached 14.7 pounds per square inch of pressure, it would turn from a liquid fuel into a gas, rendering it useless for vehicles.

Summer Versus Winter Blends

Summer fuel blends must be between 7.8 and 9.1 pounds per square inch of pressure. If the blend contains 10 percent ethanol, then the pressure level can go as high as 10.1 and still meet state and federal clean air requirements. Within New York City, the blend of fuel available in the summertime must have an even lower pressure level in order to minimize air pollution. Because summer gasoline blends are purer, they tend to cost more than the dirtier winter blends.