Blame Harvey for the extra cost to fill up your tank. Gas prices across the state of Illinois are up in the wake of the storm that cut through the Gulf of Mexico and through Houston. The price of a gallon of gas jumped about a dime yesterday. Patrick DeHaan with GasBuddy says gas prices will likely stay higher than usual for the next few weeks. Most stations in downstate Illinois are selling a gallon of regular gas for anywhere between two dollars 30-cents a gallon to two dollars 50-cents a gallon.