SOUTH PORTLAND, ME – Wright Express (WEX) posted an update on retail gasoline and diesel prices, noting that they’re expected to rise in the first half of September.

In addition, the company said the national average, $3.62 per gallon, is nearly $1.00 higher per gallon higher than it was more than a year ago. Diesel prices are at $3.89 per gallon, $2.24 higher than the same time last year. Income spent on gas is currently at 8.4 percent. Last year it was 6.7 percent.

Current issues having an impact on the market include refinery problems, with the Midwest and West Coasts being affected most significantly. EPA-mandated summer fuel is in short supply. When stations begin to switch to the winter supply and can discount summer production, WEX said prices will start to drop.

WEX said it expects diesel prices to follow this pattern and drop toward the end of September.

The table below shows average retail fuel prices on a regional basis for the month of August 2011.

Atlanta GA $3.61 $3.88
Boston MA $3.74 $4.01
Chicago IL $3.92 $3.94
Dallas TX $3.50 $3.79
Denver CO $3.44 $3.82
Detroit MI $3.75 $3.92
Houston TX $3.75 3.485
Los Angeles CA $3.80 $4.18
Memphis TN $3.50 $3.81
Miami FL $3.74 $3.95
Minneapolis MN $3.71 $3.93
New Orleans LA $3.46 $3.73
Philadelphia PA $3.68 $4.05
Phoenix AZ $3.33 $3.69
Portland OR $3.75 $3.82
San Francisco CA $3.88 $4.33
Seattle WA $3.82 $4.14
St. Louis MO $3.41 $3.71
Washington DC $3.86 $4.15
National Average US $3.61 $3.88