California gas prices are starting to slip below $4 a gallon, the first time in nearly two months they've been that low. We're now forking over 28 to 30 cents less than we were a year go.

Time to rejoice, eh? Not so fast.

"We're not out of the woods yet," said Patrick DeHaan of GasBuddy.com. "Extensive refinery maintenance continues, and should one of them fumble, prices could head the other direction again."

Some experts predict prices nationally will exceed $4 a gallon by Memorial Day, then fall in June. The current average is $3.65 a gallon across the country, compared with $4.05 in California, according to AAA, and $4.03, according to GasBuddy.com.

AAA lists prices at $4.03 in San Jose, $4.02 in Oakland, $3.98 in Vallejo, $3.97 in Santa Cruz and $3.86 in Modesto. For nearly two weeks, they've declined by a cent or more every 24 hours.

GasBuddy.com says prices are lower in every major city it tracks -- some 166 across the 50 states. Some stations in the Chicago area are selling fuel for 50 cents less than a year ago.

Lower prices have eased the grumbling of motorists from coast to coast. The price break comes as a relief after the 56-cent hike from early February to early March -- the largest one-month jump since 2008.

"We believe prices in 2013 generally won't be as nasty as 2012, with June being the month (with) the lowest gasoline prices for the summer," DeHaan said.

That suits Jim Reyes of Fremont just fine. He recently paid around $3.85 a gallon for a fill-up at the Costco store on Middlefield Road in Redwood City -- almost 60 cents less than what he paid a few weeks ago at a nearby Shell.

"I always expect high prices on the Peninsula," the 32-year-old bartender said. "Anything under $4 seems cheap. And if I had waited to get home to get gas, I would have paid even less."

One reason for slumping prices is U.S. oil output, which rose 14 percent to 6.5 million barrels a day last year -- a record increase. The U.S. is forecast to overtake Saudi Arabia by 2020 as the world's largest crude oil producer. At the same time, the U.S. demand for gas has fallen to 8.7 million barrels a day, its lowest level since 2001, as people switch to more fuel-efficient cars.

The U.S. Energy Information Administration reported Wednesday that crude inventories surged to a nine-month high as production and imports increased.

"There's plenty of supply here," Chip Hodge, managing director at Manulife Asset Management in Boston told Bloomberg News. "The positive changes in the U.S. crude-oil production picture are mind-boggling."

But as economies in Asia and Latin America expand, their energy consumption is rising, which puts pressure on fuel supplies and prices across the globe.

China, which has overtaken the U.S. as the world's largest oil importer, is now the single biggest influence on global demand for fuel. China's consumption has risen 28 percent in five years, to 10.2 million barrels a day last year.

The Chinese economy, DeHaan said, is the "800-pound gorilla in the picture now."

The Associated Press and Bloomberg News contributed to this report. Contact Gary Richards at 408-920-5335.