The average price of a gallon of self-serve regular gasoline in California is now a whopping $5.28, compared with $3.73 at the same time a year ago, according to the latest data from the American Automobile Assn.In Los Angeles County, the average gas price for regular-grade fuel is $5.37 per gallon — up from $4.67 a month ago and $3.79 a year ago, according to AAA. The national average is $4.00 per gallon.Experts say Russia’s war on Ukraine and increase in gas demand coupled with a reduction in total supply are contributing to the prices that will probably keep rising as crude prices continue to climb.Even before Russia, one of the world’s top producers of petroleum and other crude oil, invaded neighboring Ukraine and set off Europe’s largest ground war in more than 75 years, gas prices had ballooned in reaction to pandemic supply-chain issues and inflation.Eric Swanson, a professor of economics at UC Irvine, said low-income residents will be hit hardest by the rising cost in gas and housing. Eventually, he said, it will also lead to higher prices for transported goods.In many places across the Southland, they already have.Carlos Perez, who owns C.P. Towing Service in El Monte, said increased gas prices recently forced him to raise his rates for several services, including a simple tire change and hauling crashed vehicles.“That’s just the business,” he said. “Everything is going up.”Perez, 55, who runs the company on his own and often works 14-hour shifts, typically covers Los Angeles and Orange counties but sometimes makes farther pickups, he said, including one that was 700 miles away.To cover that kind of mileage, he fills up his 2016 Peterbilt flatbed truck almost every day, shelling out $200 each time — up from $160 at this time last year, he said.It has been challenging, but Perez finds encouragement from his customers’ loyalty and positive reviews.“Gas is high, but what can you do?” he said. “I’m happy work hasn’t stopped.”Times staff writers Kenan Draughorne, Andrew J. Campa and Marisa Gerber contributed to this report.