What Is Seasonal Fuel?
Since 1995 the U.S. government has required refiners to produce a special grade of gas for sale in the country's major urban areas between June 1 and Sept. 15, generally the smoggiest weeks of the year because of the way heat traps smog over urban areas.
Among other things, summer-grade gas is mixed with less butane, a change that incrementally slows the rate at which gas evaporates. The change reduces the vapors released when filling the gas tank.
Low-level ozone is a pollutant that causes smog. It's created when nitrogen oxide and volatile organic compounds interact with sunlight. Gas vapors and engine exhaust produce NOx and VOCs. Ozone harms plants and attacks people's airways, particularly children. It worsens conditions such as asthma, emphysema and bronchitis. According to the Environmental Protection Agency, prolonged exposure can result in permanently scarred lungs.
The EPA receives consumer complaints saying summer fuels cut a car's fuel economy by as much as 20 percent. However, the government says additives are capable of reducing fuel economy by only 2 to 3 percent.
Summer-grade gas is more expensive because refineries must briefly shut down to make the transition, and any fuel reformulation adds to production costs.
There is debate about how much the change actually adds to the pump price. It's up to each oil company to mix a summer fuel that performs to federal and state mandates, and industry players consider formulations and production details to be proprietary information.
Not at all coincidentally, summer blends arrive when demand for gas begins to soar. With greater demand comes a higher price. This makes it difficult to attribute a percentage price increase simply to the arrival of summer-grade gas.