(Undated) — The national average for a gallon of regular unleaded is down slightly from Friday. According to this morning’s numbers from GasBuddy.com, the national average is $3.13 a gallon, down two cents. Here in Illinois, drivers are paying an average of $3.39 a gallon, down two cents from the end of the week. Across the river in Indiana, the statewide average is $3.13 per gallon, three cents lower than Friday. Oklahoma drivers are paying the lowest statewide average $2.62, down three cents from Friday. California drivers are paying the highest at $4.51 a gallon, down a penny from Friday…