Supply shortages pushed average retail gasoline prices up more than 15 cents a gallon nationally during the past two weeks, the largest retail price hike on record since the Lundberg Survey (search) began keeping records 50 years ago.

The survey of 8,000 service stations on Friday showed an average of all grades of gasoline, including taxes, reached $1.7484 a gallon, just short of the survey's all-time high weighted average of $1.7608 set last March 21, analyst Trilby Lundberg said Sunday.

Self-serve regular gasoline showed an average weighted price of $1.7191 a gallon, with mid-grade at $1.8127 and premium grade at $1.9046.

Phoenix had the highest leap in the nation during the two-week period, with prices jumping 60.42 cents a gallon for self-serve regular. On Aug. 22, self-serve regular averaged $2.1425, the highest price in the nation for that grade.

By comparison, the lowest price for that grade was in Charleston, S.C., where the average for self-serve regular was $1.4920.

Temporary refinery shutdowns caused by the massive East Coast/Midwest blackout combined with a break in a major pipeline in Arizona to cause the supply disruptions, Lundberg said.

However, the reopening of the pipeline and the end of the blackout means gas prices should fall thanks to the traditional decline in demand in September and an influx of imported gasoline attracted by the current high prices, she said.