The United States retail diesel prices increased an average of six centst this week to $2.56, bringing the 27-day average price to $2.72. The largest increase was in the Midwest with a jump from $2.49 last week to $2.63 this week. The 15-cent rise brought the 27-day average price to $2.63. New England saw no change, while the Gulf Coast and Rocky Mountain regions had two-cent increases. The hihgest retail diesel prices in the United States were on the West Coast at $2.73, and the lowest is in the Gulf Coast region at $2.34