The bottom falling out of the oil barrel is keeping gas prices on a downward slide.
Oil futures hit a four-year low Thursday, ending the day at $43.67 a barrel, or $104 below the record $147 a barrel in July.
Gas prices declined to a national average of $1.773 a gallon for regular unleaded on Friday, down 1.6 cents from Thursday, according to the AAA daily fuel gauge report.
The state average is a half-cent higher at $1.778 a gallon, with Milwaukee drivers paying the least in Wisconsin at $1.742 a gallon, followed by Janesville at $1.753, Green Bay at $1.757, Madison at $1.775, La Crosse at $1.817 and Eau Claire at $1.892.
The low price in Madison is $1.72 a gallon at stations throughout the area, while the high price is $1.85 a gallon at a station on the city's east side, with most higher-priced stations selling regular unleaded at $1.79 a gallon, according to madisongasprices.com.
Missouri has the lowest statewide average for regular unleaded in the country at $1.566 a gallon, with 27 states selling the fuel for an average less than $1.75 a gallon.
The lowest price in Missouri for regular unleaded is in Kansas City, where drivers are paying $1.40 a gallon.
The last time gas was this low in the United States was in December 2002, according to the retail gasoline historical price charts from the Energy Information Agency of the U.S. Department of Energy.