RIVERSIDE, Calif. -

The average price of a gallon of self-serve regular  gasoline in the Inland Empire Friday recorded its largest daily decrease since  Dec. 13, dropping 1.7 cents to $4.172.

      The average price in Riverside and San Bernardino counties has dropped  for 15 consecutive days and is 7.1 cents less than one week ago, 1.1 cents  lower than one month ago and 20.3 cents below what it was one year ago,  according to figures from the AAA and Oil Price Information Service.

      The average price rose 30 times in the 31 days preceding the streak of  declines.

      Prices at the pump have been dropping because most California refineries  have concluded scheduled maintenance without experiencing any major incidents before the switch to summer-blend production, leaving adequate gasoline supplies, said Jeffrey Spring of the Automobile Club of Southern California.