Updated

The average gasoline price nationwide for all grades dropped less than 2 cents in three weeks, continuing a slide in pump prices that began in April, an industry analyst said Sunday.

The average retail price for all three grades dropped 1.65 cents to $2.16 per gallon between May 20 to Friday, said Trilby Lundberg (search), who publishes the semimonthlyLundberg Survey (search) of 7,000 gas stations around the country.

The most popular grade, self-serve regular, was priced at $2.13 a gallon, while customers paid $2.23 for midgrade. Premium averaged $2.33 a gallon for the period.

The average price for all grades nationwide has dropped 16 cents since April 8, although it is still 12 cents higher than the same time last year.

Lundberg said she expects prices to continue to drop, although the pace has slowed because of rising demand for diesel fuel as the economy recovers. Demand for diesel has propped up crude oil prices, which recently gained strength, but has moderated in the past few days.

"That, combined with the fact that there is plenty of gasoline, will allow for some further declines at the pump, I believe," Lundberg said Sunday.

The highest price for unleaded regular in the nation among the stations surveyed was in Honolulu at $2.44. The lowest was in Charleston, S.C., at $1.99

In California, the average price for unleaded regular fell 13.5 cents in three weeks to $2.307.

Lundberg said gas prices tend to spike higher in California as refineries gear up for summer demand by processing the more expensive anti-pollution formulas required in the state. Subsequently, California prices drop faster than the national average.

The highest price for unleaded regular in the state among stations surveyed was in San Francisco at $2.33. The lowest price was in Sacramento at $2.23.