evidence: Mapped: Gas Prices in Every U.S. State [...] Meanwhile, West Coast states dominate the list of jurisdictions with more expensive gas. With high local taxes and a unique gasoline blend designed to reduce emissions but which increases prices, California tops the list. [...] This is because gasoline prices often rise during peak driving seasons, such as summer, when more people embark on road trips and travel. In addition, gas stations switch to a less expensive winter blend of gasoline after September.