U.S. drivers continue to be hit with sticker shock at the pump as gasoline prices jumped to record highs for the fourth week in a row, the Energy Department's statistical agency reported on Monday. The national average retail price for unleaded gasoline soared 5 cents from last week to $1.681 a gallon, based on the Energy Information Administration's weekly survey of 800 service stations. The pump price is up 56 cents a gallon from last year and the highest since the EIA began tracking weekly fuel prices a decade ago. The price for gasoline has risen 16.2 cents over the last month because of high crude oil prices and tight supplies for gasoline during the summer driving season. The national price for cleaner burning reformulated gasoline is up 2.4 cents to $1.70 a gallon. Midwest drivers continued to pay the most for fuel, with the price for conventional gasoline up 7.8 cents to $1.874 a gallon. The Federal Trade Commission is investigating why Midwest gasoline prices are the highest in the nation. U.S. Energy Secretary Bill Richardson has said the government must determine if oil companies are gouging customers at the pump.