With Southern California gas prices topping $4 for the first time since 2015, many have been quick to place the blame on refinery problems and a switch to the summer blend of gas.

Both clearly figure into the mix. But the Golden State’s broad array of gas taxes and a “mystery surcharge” no one can quite explain placed California motorists at a disadvantage to begin with.

Here’s a breakdown of what we pay in gasoline taxes, according to the California Energy Commission. All numbers except the final category have been rounded to the nearest penny and were effective as of March. The combined Cap & Trade and low Carbon Fuels Standard costs were effective April 12.

Federal excise tax — 18 cents

— 18 cents State excise tax — 42 cents

— 42 cents State and local sales tax — 8 cents

— 8 cents State underground storage tank fee — 2 cents*

— 2 cents* Additional costs for compliance under Cap & Trade, as well as the Low Carbon Fuels Standard — 28 cents

— 28 cents Total — 98 cents

* Note: The state and local sales tax is calculated at an average state sales tax rate of 2.25% percent although actual sales tax rates vary throughout California.

The ‘mystery surcharge’

Severin Borenstein, a professor at UC Berkeley’s Haas School of Business and faculty director of the Energy Institute at Haas, said his own tax calculations came within a penny of that total. But the mystery surcharge — an added expense that has yet to be identified — has averaged 28 per cents a gallon from January through March of this year. When added to the taxes, that brings the total to about $1.26 a gallon.

“In January, a group of 19 state legislators sent a letter to the California Attorney General’s Office saying, ‘We want you to investigate this,’ ” Borenstein said. “They have never replied. They said they don’t make public statements about investigations. We don’t even know if they are investigating it.”

No luck in tracking it down

Borenstein previously served as chairman of the state Petroleum Market Advisory Committee. The panel was formed by the California Energy Commission to look into price spikes.

“We spent two years trying to find out what that mystery surcharge was, but we couldn’t dig deep enough to get that information,” he said.

Borenstein said the committee had no power to compel people to talk. Moreover, it had no resources or staffing to investigate.

“The committee disbanded because California’s open-meeting rules made it very difficult for the five of us — who were located all over the state — to get together,” he said.

The money is going to companies somewhere in the supply chain, Borenstein, said, but no one has been able to track it down.

The surcharge may be a mystery, but the economic fallout isn’t. Borenstein said it’s costing California drivers $11 million a day, or $4 billion a year.

“We have paid about $20 billion through this mystery surcharge since the Torrrance refinery fire in 2015,” he said. “That works out to about $500 per person.”

Possible causes

Borenstein hasn’t determined what might be fueling the mystery tax, but he has some theories.

“If you look at our gas usage, it’s been climbing since 2014,” he said. “That pushes capacity constraints on the system, which means we need more imports. But I’ve heard that port space and storage space at the ports has been harder to come by.”

Borenstein also noted that the Chevron and Andeavor, which each own multiple refineries in California, produce about half the state’s special blends of winter and summer gas.

“In antitrust terms that’s a pretty big concern,” he said. “You wonder if imports are really flowing freely into this market.”

Things could be worse. In Hong Kong, drivers pay the equivalent of $8.26 in U.S. dollars per gallon. Other high-priced countries include Norway ($7.34), Greece ($6.94), Denmark ($6.89), Sweden ($6.77) and Italy ($6.72).

When the price hikes started

Southern California gas prices began inching up when refineries slowed their operations last month to do scheduled maintenance and switch from their winter blend of gas to California’s specially formulated summer blend, which is environmentally more stringent and designed to reduce greenhouse gas emissions.

That happens every year.

But prices escalated rapidly after Valero Energy Corp.’s refinery in the Bay Area stopped processing oil after a week of smoky emissions prompted air quality warnings. Things got worse as the result of a fire at the Phillips 66 refinery in Los Angeles and technical issues at Chevron Corp.’s El Segundo plant.

Relief on the way?

Those factors — combined with California’s already high gas taxes — conspired to push prices well beyond the comfort level for most California consumers and businesses. Still, things should be looking up soon, according to Jeffrey Spring, a spokesman for the Automobile Club of Southern California.

“I think we’ll get some relief in next couple or three weeks,” Spring said. “Refinery issues tend to be relatively short-lived. I know the Phillips 66 refinery should be opening up their units again in 2 ½ to three weeks and by then we should see a couple ships bringing in more of California’s specially formulated gas. That should help reduce prices.”

High prices

Meanwhile, Southland drivers are paying some of the highest prices they’ve seen in years.

On Tuesday, Los Angeles County’s average price for a gallon of regular gas was $4.07, up 70 cents from a month earlier. Orange County was close behind with an average of $4.05 per gallon, and prices in San Bernardino County ($3.98) and Riverside County ($3.99) weren’t much better.

But as Southern California drivers know, it can get worse — a lot worse.

Four Union 76 stations in Pasadena, Santa Monica, Los Angeles and Beverly Hills were selling regular for a whopping $4.89 a gallon on Tuesday.

On the flip-side, a Sam’s Club in Ontario was selling regular for $3.64 a gallon and a Costco in Irvine posted regular for $3.75 a gallon.