Prices at the pump soar 15.5 cents to average $1.72 a gallon, survey finds.

Gas prices zoomed at a record pace over the last two weeks, increasing by 15.53 cents a gallon to a national average of $1.72, according to a national survey of gas stations.

That was the largest two-week rise in the half-century history of the Lundberg Survey, Publisher Trilby Lundberg told CNN.

Still, the price was a penny shy of the all-time high, which was on March 21, 2003, she said.

Lundberg said panic buying in Phoenix after a pipeline burst Aug. 8, cutting supplies to the area, caused prices there to soar 60 cents per gallon, to $2.12. Phoenix consumers paid the most in the nation for gasoline, according to the survey.

The rupture affected prices all along the West Coast, driving the average cost of a gallon of gas in Los Angeles up 42 cents to $2.06.

Refinery shutdowns caused by last week's blackout in the East and Midwest also played a role in the price jump, she said.

The survey of prices at about 7,000 gas stations was carried out Aug. 8 and Aug. 22.

Lundberg predicted that the pipeline's repair and the drop in demand that typically occurs at summer's end would send prices lower in coming weeks.

Here are some other prices across the nation: Charleston, S.C., paid the least, at $1.49; El Paso, Texas: $1.59; Birmingham, Ala. $1.61; Detroit: $1.74; Chicago: $1.83, Sacramento, Calif. $2.02; Miami: $1.68; Hartford, Conn. $1.62, and Philadelphia: $1.64.