Gasoline prices trended downward in St. Louis this past week. According to GasBuddy.com, prices have fallen 11.3 cents per gallon, averaging $3.20 a gallon on Sunday. GasBuddy surveys nearly one-thousand gas outlets in St. Louis everyday. The national average has fallen 4.5 cents per gallon in the last week to $3.49 per gallon. Yesterday's prices in St. Louis were 38.9 cents per gallon lower than the same day one year ago and 35.1 cents per gallon lower than a month ago.