NEW YORK (AP) -- The average price of gasoline soon could surpass $4 per gallon nationwide. It's already $3.93 per gallon, a record for this time of year.

Why the seasonal spike? It's the time of year refineries reduce output to repair equipment and start making a cleaner, more expensive blend of gasoline for summer.

The National Association of Convenience Stores says since 2000, pump prices have risen every year between early February and late May.

The annual increase has boosted prices by 27 percent on average, but this year, prices have risen 14 percent since Feb. 1.

Tom Kloza, chief oil analyst at Oil Price Information Service, says the built-in increase in prices is accentuated this year because of strong global demand, heightened tensions with Iran and a smattering of supply disruptions that have kept crude oil prices elevated for months.

Also this year's spring surge is more extreme than usual because three refineries that serve the East Coast were shut down last fall and another one may be closed in July.