Seasonal temperatures and government regulations make a big difference in the type of gasoline we use in our vehicles.

SUMMER GASOLINE

In the warmer months, gasoline has a greater chance of evaporating from your car’s fuel system. This can produce additional smog and increased emissions. Refiners reduce the chance of gas evaporation in your car during the summer by producing gasoline blends that have lower Reid vapor pressure (RVP), or lower volatility. These blends vary from state-to-state, region-to-region due to RVP state regulations. They also vary by octane level.

Cost for your wallet: According to NACS, this higher-grade fuel can add up to 15 cents per gallon to the cost of your fill-up. This excludes the increased cost due to summer fuel demand, which can vary between 5-15c/gal, depending on region. More stringent requirements (like California) can mean an even higher cost.

WINTER GASOLINE

In winter, gasoline blends have a higher Reid vapor pressure, meaning they evaporate more easily and allow gasoline to ignite more easily to start your car in cold temperatures. This blend is cheaper to produce, which results in lower gas prices at the pumps from late September through late April.

Cost for your wallet: Prices typically fall 10-30c/gal starting in mid/late September through late November as gas stations switch to winter gasoline and demand for gasoline falls seasonally as we start to stay closer to home. Many retailers continue to sell summer gas until their inventories run out before then selling winter gasoline. Hurricane season can also affect prices before the switch, ending in a squeeze just before the switch since refiners don’t want excess expensive summer gasoline sitting around and especially if refineries are in the path of a major storm.

FUELS CALENDAR: DATES YOU NEED TO KNOW

March-April: Refineries begin to produce summer gasoline blends. More than 14 different blends are produced during this period, due to different state regulations for reformulated gasoline and Reid vapor pressure requirements.



May 1: Fuel terminals are required to sell only summer gasoline on May 1, while gas stations have until June 1 to complete the changeover to summer gasoline. The switch from winter to summer gasoline is one of the major factors behind seasonal fuel price increases in May.

September 15: The last day that EPA requires summer gasoline is September 15, but most refiners start producing it again in late August and will draw down remaining summer supply. In addition, gasoline demand falls as temperatures begin to seasonally drop, leading gas prices to fall throughout the fall. Starting Sept. 16, gas stations can again start filling up with the non-summer, or “winter” gasoline.