Reason No. 4: Cheaper blends in winter
Did you know that there are many different recipes for gasoline? Thanks to different state and local regulations, your neighborhood pump probably sells a different blend of gas than pumps in other states. And there are seasonal varieties, too -- summer gasoline and winter gasoline.
Winter gasoline is usually the cheapest.
Every September, the government starts to ease off clean-air standards for oil refineries, allowing them to make gasoline with cheaper hydrocarbons like butane. Refineries would love to benefit from the cost savings, but they usually don't. Petroleum traders know they can buy gasoline at lower prices without hurting the refinery's profits, and prices usually drop in response, says Tom Kloza, the chief oil analyst at GasBuddy.com.
Refineries usually begin making cheaper "winter-blend" gasoline between September and October every year. Americans will pump it into their tanks until spring.