Regional refinery issues in the United States means average gas price trends are flirting with a historical move upward, market analysis finds.

Though unchanged from the previous day, the $2.29 national average retail price for a gallon of regular unleaded for Tuesday is 11 cents, or about 4.6 percent lower, than one month ago. In a weekly market report, motor club AAA reports, however, the national average price holding steady for 13 straight days.

Prices in the Midwest may be holding the national average price higher. Three of the 10 states with the highest national average price are in the Midwest, with Ohio reporting a 17 cent spike in prices from one month ago.

Refineries starting in mid-September are able to produce a winter blend of gasoline, which because of fewer environmental restrictions, is cheaper to make. That, and lower demand than during summer months, should translate to lower prices at the pump.

"Averages in the Midwest have been under pressure, due to both planned and unplanned maintenance, at some of the region's major refineries, and prices should remain relatively volatile as the maintenance continues," the motor club said in its report.

Refinery maintenance may be elevated because of higher consumer demand for gasoline during the summer.

States along the West Coast, meanwhile, are reporting the steepest declines, with California and Washington both posting 35 cent declines from one month ago.

Separate analysis from retail price-watching website GasBuddy.com finds a national price spike in October is rare.

"Only once in the past five years have we seen gas prices climb in October," its weekly emailed report read.

Both analyses forecast a national average price for gasoline at or near the $2 per gallon mark before the end of the year. Three states -- South Carolina, Mississippi and New Jersey -- are already below that level.