The difference between the highest and lowest state average annual retail gasoline prices for 2019 was $1.41, with Hawaii having the highest average annual price ($3.67/gallon) and Mississippi having the lowest ($2.26/gallon). In general, the western-most states and northeastern states had higher gasoline prices than the rest of the country. Wyoming had the median average annual retail price of $2.56/gallon.
Source: GasBuddy, Fuel Insights, 2020. Daily price data for 2019 analyzed by David Gohlke, Argonne National Laboratory.