LOS ANGELES -- The utility whose leaking natural-gas well has driven thousands of Los Angeles residents from their homes acknowledged Thursday it understated the number of times airborne levels of the cancer-causing chemical benzene have spiked during the crisis.

Southern California Gas Co. had been saying on its website and in emails to The Associated Press just two air samples over the past three months showed elevated concentrations of the compound. But after the AP inquired about discrepancies in the data, SoCalGas admitted higher-than-normal readings had been found at least 14 times.

SoCalGas spokeswoman Kristine Lloyd said it was "an oversight" that was being corrected. The utility continued to assert the leak has posed no long-term risk to the public.

Public health officials likewise have said they do not expect any long-term health problems. But some outside experts insist the data is too thin to say that with any certainty.

"I have not seen anything convincing that it's been proven to be safe," said Seth Shonkoff, the executive director of an independent energy science and policy institute and a visiting scholar at the University of California, Berkeley. "I'm not going on record as saying this is absolutely an unsafe situation; I'm saying there are a number of red flags."

The leak at the biggest natural-gas storage facility west of the Mississippi River was reported Oct. 23. The cause is unknown, but the leak has spewed huge amounts of methane, a potent greenhouse gas, and occasionally blanketed neighborhoods about a mile away with a sickening rotten-egg odor.

SoCalGas has run up more than $50 million in costs so far in trying to contain the leak and relocate about 4,500 families. Gov. Jerry Brown has declared an emergency, and some environmentalists are calling it the worst environmental disaster since the BP oil spill in the Gulf of Mexico in 2010.

Health officials and SoCalGas have said most of the gas has dissipated, though the odor from the chemical additive that makes the methane detectable is blamed for nausea, headaches and nosebleeds.

Natural gas contains smaller amounts of other compounds, such as benzene, that cause cancer and other illnesses.

In the Los Angeles area, benzene normally is present at minuscule levels of 0.1 to 0.5 parts per billion, according to the South Coast Air Quality Management District. But SoCalGas has been saying on its website the typical background level is 2 parts per billion.