"At that price it continues to be an item that crooks are finding great opportunity in stealing. Every county is being hit," William Yoshimoto of a Californian agricultural crime unit told the state's farm bureau. "It is a crime of opportunity right now. The prices are elevated and they can get a very fast return for little risk."
Don Morelli, a dairy farmer, told the farm bureau that he realised something was amiss when all the keys to his farm vehicles were missing. They had been used to open petrol caps and fuel tanks.
"There were pieces of rubber hose lying around which they used to siphon fuel out of the tanks," Mr Morelli said. "This is the third or fourth robbery we've had and we don't feel safe and secure any more."
Most thefts take place at night in farmyards, but there have also been increases in people driving away from petrol stations without paying and in thefts of fuel from cars.
A side-effect of the thefts has been a rise in the sale of lockable petrol caps. AutoZone, the largest car accessory retailer in the US, reported sales of locking fuel tank caps were up 60% in one week last month to 10,000. The owner of a car parts shop told the Seattle Times: "Everybody knows that an SUV is going to have 25 gallons of gas in there. Jackpot."