Tumbling oil prices continue to drive down fuel costs, with diesel posting a ninth consecutive weekly decline.The average U.S. retail pump price for diesel was down 3.4 cents in the Jan. 11 report by the Energy Information Administration (EIA), to $2.177 per gallon. The price is about $0.88 per gallon cheaper than this time last year and the lowest price since March 2009.Prices were down in every region of the country, paced by the Rocky Mountain region where a gallon of diesel was down 5.7 cents $2.134.The West Coast less California saw a 4.5 cent decline to $2.258. Otherwise, California registered 3.3 cent fall to $2.562, still the highest price in the contiguous 48 states.New England reported a 0.9 cent drop to $2.335, while the diesel price fell 4.1 cents in the Central Atlantic to $2.35, and 2.7 cents in Lower Atlantic region to $2.116.In the Midwest price was down 3.4 cents to $2.096 and the Gulf Coast reported a 3.4 cent drop to $2.08, the lowest price for a gallon of diesel in the nation. The national average price for gasoline fell below two bucks, down 3.2 cents to $1.996.