Gas prices in California rose as much as 20 cents per gallon between Thursday night and Friday morning, and the state's fuel shortage is just one reason U.S. gas prices will flirt with $4 for a while.

The average price of a gallon of regular gasoline in California is nearly $4.49, according to the AAA Daily Fuel Gauge Report. That's the highest in the country and far exceeds the roughly $3.89-a-gallon national average reported by the Energy Information Administration -- still a record for this time of year.

"We do not know when we will be resupplied," read a sign at one Southern California Costco, according to the Times. 

In some areas of the car-happy state, prices have jumped 40 cents in a week as refinery problems have created shortages and helped send wholesale prices soaring. Among the recent disruptions, an Aug. 6 fire at a Chevron (CVX) refinery in Richmond has one of the region's largest refineries producing at reduced capacity. A power failure in Southern California has affected an Exxon Mobil refinery, and a Chevron pipeline that moves crude to Northern California also was shut down.

While all of the above is putting pressure on California pumps, other forces far beyond the state's borders are fueling price increases and a sticky nationwide slide from $4 a gallon. There hasn't been a refinery built in the U.S. since 1976, which means each time one goes offline for a bit or shuts down, the gap between crude oil and gasoline supplies widens. Commodities brokers know this all too well and are starting to place huge bets on commodities futures as peak winter heating demand nears.

As noted by Fortune, a recently released United Nations report explicitly states that the "financialization" of commodities markets -- "hundreds of billions of dollars of bets placed on expectations of temporarily rising prices" for energy, food and other goods -- is the "root cause" of elevated prices. That's right, a bunch of folks sitting at home barking orders to traders as if it were a scene from "Trading Places" helped boost gasoline prices, which in turn pushed this summer's global oil prices 65% higher than the averages reached during the commodity price boom of 2003 to 2008.

"Investors treat commodities as an asset class, which means that they are betting on a certain price trend during the period they are invested in commodity assets," the UN said. "They do not trade systematically on the basis of fundamental supply and demand relationships in single markets, even if shocks in those markets may influence their behavior temporarily."

In a fuel market in which drivers already think prices are headed toward $5 a gallon, commodities brokers and investors aren't just potentially funneling populist anger away from fuel companies and toward Wall Street. They're building that anger a pipeline.