How does an L.A. motorist know that 20 gallons of gasoline has really been pumped into his car and not 18 or 19? With the county facing a shortage of inspectors for its thousands of gas pumps, the short answer is that he doesn’t.

Last week, the County Board of Supervisors approved a plan to fund the hiring of 20 more inspectors to provide annual checks on all meters and scales. The inspectors will be funded through increased fees on gas station owners, grocery stores and other business establishments with meters and scales.

“We need to ensure that consumers receive what they are paying for,” said County Agricultural Commissioner Kurt Floren, who also is the director of weights and measures.

The fee hikes, which will be phased in over the next three years, stem from a state law passed earlier this year that was sponsored by Assemblyman Ira Ruskin, D-Redwood City, and allows counties to gradually raise fees levied on retailers to fund the hiring of more inspectors.

Overall, the fees will nearly triple over the next three years, to a total of $4.7 million. The new fees will range from $60 to $100 per site, plus $12 to $20 per measuring device.

The number of meters for gasoline dispensing nozzles alone has doubled in the last 10 years to about 55,000, according to Deputy Agricultural Commissioner Bob Atkins. (The number of gasoline stations has dropped during that time, but many pump stations now have six meters for two nozzles, instead of two.)

“We see a fairly consistent failure rate of about 1.5 percent in gas dispensing meters,” Atkins said. “It’s just that the number of meters has exploded.”

Also, as new retail establishments open and computerization increases, the number of meters and scales has grown. While supermarket checkout scanners are covered under a different inspection program, the computerized scales in checkout lines and meat counters also need to be monitored.

What’s more, as the region’s truck traffic has grown, so has the need to weigh the contents, both at truck scales and when the contents are off-loaded at local warehouses. There are about 540 truck scales in the county, nearly double that of 10 years ago, Atkins said.

Despite this explosive growth, the county hasn’t raised the fees on meters since 1994. That’s because state law prohibited any fee hikes.

Ruskin had originally pushed for an immediate hike but met with resistance from the California Retailers Association, the California Grocers Association and the California Service Station and Automotive Repair Association. The organizations argued that it would place an undue burden on businesses. They also pushed for a cap on fees for multiple meters and scales at a site. The legislation was later revised.

“We have always agreed that fees needed to be raised so that there could be more inspectors,” said Dave Heylen, spokesman for the California Grocers Association. “There were just some specific items in the bill that we felt needed to be worked out.”

But the service station group wasn’t satisfied with the revised bill.

“We think this increase is ridiculous. There may be some counties that need more inspectors and Los Angeles may be one of them but to give carte blanche to all counties to raise fees to pad their budgets is not warranted,” said Dennis DeCota, the executive director of association. “This is just another fee that will be passed on to the consumer, on top of the already outrageous cost of product.”

In Los Angeles County, inspectors are sent out both in uniform and undercover.

“At gas stations, the biggest problem is not the price being charged per gallon. It’s making sure the pump actually dispenses the number of gallons indicated,” said Jeff Humphreys, who heads up the county’s weights and measures inspection program.

Humphreys said most of the violations are the result of negligence. Sometimes, old equipment may leak, causing some loss of gasoline. Other times, the gallon and price meters continue to run after the nozzle shuts off, charging the customer for gasoline not pumped into the car, he said.

As for intentionally defrauding customers, Humphreys said there hasn’t been a clear-cut example since 1998, when Mepco Oil agreed to settle a case in which it was charged with installing microprocessors that systematically overcharged customers and evaded detection.