The average price of a gallon of self-serve regular gasoline in the Inland Empire dropped Tuesday to its lowest amount since Dec. 28, falling six-tenths of a cent to $3.57.

   The average price in Riverside and San Bernardino counties has fallen 21 consecutive days and 61 of the past 62, according to figures from the AAA and Oil Price Information Service. It is 3.2 cents less than one week ago, 18.3 cents lower than one month ago and 22.9 cents below what it was one year ago.

   The dropping pump prices are the result of lower wholesale prices and  the Nov. 1 switch to winter blend gasoline, which costs less to produce, according to Jeffrey Spring of the Automobile Club of Southern California.