According to the Iowa Department of Agriculture and AAA-Iowa, natural gas was the only tracked fuel to see an increase in price over the past week. As of Wednesday, Dec. 14, the price of a gallon of regular unleaded gasoline was down 16 cents to $2.91, 14 cents lower than a year ago. The national average on Wednesday stood at $3.21 per gallon, a 15-cent decrease. The state’s retail diesel average dropped 21 cents to $4.49 per gallon compared to $3.33 a year ago. The national average for diesel stood at $4.86. Wholesale ethanol and propane prices held steady at $2.16 and $1.94 per gallon, respectively. Home heating oil prices were down four cents to $4.07 per gallon. Natural gas prices at the Henry Hub reporting site jumped 90 cents to $6.39 per MMBtu.