WASHINGTON, D.C. --- After four straight weekly increases, the U.S. average retail price for regular gasoline dipped 0.9 cent to $3.209 per gallon as of May 28. That's 34.2 cents per gallon higher than this time last year, reported the Energy Department's Energy Information Administration (EIA). But prices were mixed across regions of the country. East Coast and Rocky Mountain prices rose. East Coast prices increased 0.1 cent to $3.098 per gallon, and Rocky Mountain prices increased 1.1 cents per gallon to reach $3.276 per gallon. In the Midwest, prices declined 0.6 cent to $3.320 per gallon, while prices for the Gulf Coast fell 2.5 cents to $3.067 per gallon. West Coast prices were down 2.3 cents to $3.349 per gallon. The average price for regular grade in California was down 2.9 cents to $3.407 per gallon, but remains 14.1 cents per gallon above last year's price. Retail diesel prices rose, increasing 1.4 cents to $2.817 per gallon. However, prices were 6.5 cents per gallon lower than at this time last year. East Coast diesel prices rose 1.3 cents to $2.811 per gallon. In the Midwest, diesel prices were up 1.0 cent to $2.783 per gallon, while the Gulf Coast saw an increase of 2.9 cents to $2.776 per gallon. The only region to see a decrease in diesel price was the Rocky Mountains, where prices were down 1.3 cents to $2.980 per gallon. Diesel prices on the West Coast saw an increase of 1.8 cents to $2.939 per gallon, while California prices rose 2.0 cents to $2.975 per gallon --- 25.2 cents per gallon lower than at this time last year.