It’s Costing Motorists More Than Ever To Fill Up Their Gas Tanks This Week. The National Average Of $2.76 Per Gallon Is The Highest Daily Average Since July 2015. Tennessee Gas Prices Set A Fresh New 2018 High, With An Average Of $2.55. Among The Most Expensive Gas Price Averages In Tennessee Are In Kingsport And Bristol, Where Drivers Are Paying An Average Of $2.59 A Gallon This Week.