Here’s a possible reason to fill up the family car before New Year’s Day: the state gasoline tax is going up.

It will rise by six-tenths of a penny per gallon, reaching 30 cents per gallon for gasoline or diesel.

That is on top of the federal fuel tax that is 18.4 cents per gallon for gasoline and 24.4 cents for diesel.

So the total tax on a gallon of gasoline in Utah will be 48.4 cents.

State law requires the Utah Tax Commission to reset the state gas tax once a year on Jan. 1.

It is set at 16.5 percent of the statewide average motor fuel rack price (the price charged by refineries to retailers) for the previous year.

The tax commission issued a bulletin saying that formula resulted in the six-tenths of a cent increase for the coming year, up from the previous 29.4 cents a gallon.

In the past, consumers griped that some gasoline retailers used tax hikes as an excuse to raise prices higher than needed to cover them. And retailers complain that they often must absorb tax hikes without raising prices to compete with others.

“Whenever taxes go up, retail profits go down,” said John Hill, executive director of the Utah Petroleum Marketers & Retailers Association.