Retail gasoline prices are on the rise again after five straight weeks of decline. The new increases are adding to the pain of historically high fuel costs for this time of year.

In California, which has returned to its customary position as the most expensive state for fuel in the 48 contiguous states, the average cost of a gallon of regular rose 4.8 cents over the past week to $3.853. The numbers are courtesy of the AAA Fuel Gauge Report, which uses retail receipts from more than 100,000 service stations around the U.S.

A year ago, the average price for a gallon of regular gasoline in California was $3.149, the AAA said. In the past year, that means the cost of filling a typical 15-gallon tank has gone up by $10.56.

Nationally, the price was also on the rise, up 6.7 cents over the past week to an average of $3.462 for a gallon of regular gasoline. A year ago, the national average was just $2.834 a gallon.

One major reason for the increases was the fact that the U.S. is exporting a considerable amount of fuel overseas, leaving the nation's supplies more vulnerable to sudden price bumps if there are any refinery outages.

"Highlighting what I've reiterated for weeks, we're seeing gasoline prices continue their volatile trend, and this time that trend is upward," said Patrick DeHaan, senior petroleum analyst for GasBuddy.com, where members report the lowest and highest prices they see.

"Over the next week, we'll see a continued rise in gasoline prices," DeHaan added.