A gas station in Santa Monica, CA.

Motorists in several parts of the country, notably including Southern California, have seen fuel prices surge past the $4 mark, with many industry observers predicting the country could soon see costs surge past the record figures set during the mid-2008 fuel scare.

With the situation only getting worse in Libya, one of the world’s largest sources of petroleum, analysts are now speculating not just if, but when pump prices in the U.S. could tip the $5 mark.  Economists are also worrying what the rapid rise might mean to an American economy that still seems fragile after one of the worst recessions in more than half a century.

As of Friday, the Lundberg Survey found that U.S. fuel prices had risen 32.7 cents over the previous two weeks, to an average of $3.51 a gallon for self-serve regular.  That’s the biggest jump the American market has experienced since a 38-cent run-up between August and September 2005, according to the Lundberg Survey, which follows fuel prices in the continental U.S.  That prior record was the result of the damage done to Gulf Coast refineries by Hurricane Katrina.

“This time around, the damage comes not from nature but from people,” said Trilby Lundberg, referring to the Libyan crisis and the broader uncertainty about Mideast oil supplies as the democracy battle rages across northern Africa.

The average price for mid-grade gasoline is $3.64, according to the survey, and $3.75 for premium.  Diesel, meanwhile, has jumped 29 cents, to $3.88 a gallon.

Among the cities surveyed, Billings, Montana had the lowest price for regular, at $3.15.  The lowest figure found in California, however, was $3.70 a gallon.  And initial reports suggested that fuel prices surged again over the weekend.

There have been plenty of forecasts that gas would top $4 across the country by Memorial Day, though that could happen sooner, analysts warn.  And what once seemed the unlikely forecast of $5 a gallon by 2012, from former Shell President John Hofmeister, is now appearing more and more a real possibility.

It has been only weeks since benchmark crude oil prices tipped $100 a barrel but as of Monday morning, Ice Brent crude had risen another $1.13 to $117.10 a barrel, with analysts predicting the upward trend was only likely to continue – at least as long as the stalemate continues between pro-Qadaffi forces and the Libyan rebels who now control much of the country’s oil production and shipping sites.

That country has the largest known oil reserves in Africa and though it supplies only 3% of U.S. petroleum, Libya is a major source for Europe, especially Italy.  As shipments dry up, users are forced to find alternative sources which only drives up prices charged by all suppliers.

In the past, the shortfall might have been offset by the fact that the U.S. market still hasn’t fully recovered from the recession, but demand for energy is now being driven by the booming Chinese and Indian economies.

The danger is that the rise in fuel prices could tamp off the nascent American recovery, cautioned Lundberg.  “Higher prices today are certainly capable of (bringing) bad news in the economy,” she said.

Chris Lafakis, the energy and financial markets economist at Moody’s Analytics, warned CNBC, this morning that the impact on consumers’ pocketbooks will be significant: an added $46.3 billion in gasoline costs over the next year if the current price of petroleum holds.

The pain will be felt at more places than just the pump.  Moody’s predicts that those who use oil for home heating will watch their bills rise a collective $18.4 billion.  And airlines, like Delta, are already bumping up prices by $10 or more per flight to cover their additional fuel costs.

Yet Lafakis said he is not as worried as such forecasts might suggest.  He sees the ongoing run-up in petroleum prices as “unsustainable (at) this magnitude.”

For one thing, analysts note that Saudi Arabia has more than enough capacity to make up for the Libyan shortfall.  But even that nation, a staunch ally of the U.S., is experiencing some political turmoil.  And unrest traditionally translates into petroleum price spikes.  How much longer the current run-up continues – and how high prices will go – remains to be seen.