As a result, the average Michigan driver with a 14-gallon tank pays $108.41 more in gas tax per year than the national average. GasBuddy, Stevens said, reported that gas prices in Michigan were around $3.95 per gallon on July 15. Stevens said that shutting down the pipeline would affect gas prices in the state. Geography plays a role in gas prices, Stevens said. Gas prices in Washington rose between 48 and 58 cents per gallon after the state adopted that program, the institute report says.