Drivers in Southern California awoke Friday to find that their gasoline prices had spiked by nearly 20 cents a gallon overnight as a result of fuel shortages caused by a series of refinery disruptions in recent weeks.

Some gas stations around the Los Angeles area were forced to shut off their pumps because of rationing by suppliers, and they displayed makeshift signs explaining that the shortages were not their fault. Drivers formed long lines at stations that did have gas, with some stations raising prices to more than $5 a gallon for regular gasoline.

“What are they doing to us?” said Marilyn Tucker, a FedEx employee, as she stopped pumping at a central Los Angeles gas station at $37, well before the tank of her sedan was full. “It’s just ridiculous.”

Prices had been rising for several days, making California the most expensive state for gasoline. On Friday, Californians paid an average of $4.49 a gallon for regular — 70 cents above the national average. Nationally, gas prices have risen less than half a penny a gallon over the last week, with prices now easing in many states.