The rhetoric in the 16th Senate District race has officially grown noxious.

"Leticia Perez has a case of bad gas," says the female narrator of a radio ad that hit the airwaves in Fresno and Bakersfield Tuesday.

The last word in the sentence is punctuated with a whoopie-cushion sound, one of three such sound effects in the advertisement.

"No. Not that kind of gas," the woman goes on, "but the kind that happens when a politician sells out to big oil, which smells just as bad."

Perez, a Democrat and former staffer for state Sen. Michael Rubio, denounced the advertisement Tuesday, two weeks before the special election to replace Rubio.

"Andy Vidak's campaign and his supporters have gone so over the top in their personal attacks on me and my family," she said. "It's hard to imagine how anybody can take him seriously as senator."

Perez said Republican opponent Vidak has "a duty and responsibility to lead" his supporters and denounce the "outrageous" and "over-the-top" attacks.

Tim Orman, an official with the Vidak campaign, said Perez should take her own advice.

"Andy's run a positive campaign from the beginning. He will continue through the election," Orman said. "The negative ads have come from the other side. We welcome her call for a positive campaign."

The new radio advertisement, funded by the Lincoln Club of Fresno County, attacks Perez's connection to Rubio, who resigned abruptly in February to take a job with Chevron Corp., irking many constituents.

Chevron contributed $250,000 to Californians for Jobs and a Strong Economy, which spent nearly that much in the May 21 primary race to support Perez.

"Chevron regularly supports candidates, organizations or ballot measures committed to economic development, free enterprise and good government," Chevron representative Morgan Crinklaw said in a statement. "We did make contributions to Californians for Jobs and a Strong Economy, which supported a pro-business, pro-industry Democrat in the primary."

Crinklaw said the corporation has no plans to repeat its aid in the current runoff battle, which ends on July 23.

"Chevron's contributions on April 16 and June 12 were for use in the May primary election. We have made no donations for the July runoff election nor do we intend to do so," the company said in the statement.

Chris Tapio, a consultant with Californians for Jobs and a Strong Economy, said the group would not get involved in the runoff.

So far, Perez has raised $636,728 for the runoff, according to reports filed with the California Secretary of State's office. Filings show Vidak has raised $596,101.

Fresno County Lincoln Club Political Director Tal Cloud said he funded the ad himself with the help of some other small donors. He's working to raise more money to keep the advertisements on the air.

In Bakersfield the ads are running on the KKBB and KNZR radio stations, Cloud said.

Cloud said two versions of the advertisement are on the air -- one with three flatulence sound effects and one with none.

As time goes on, he said, he will replace the ad with less windy sound effects.

"I'm trying to get people to laugh, because if they laugh, they pay attention," Cloud said.

He's hoping the information in the advertisement will stick with listeners.

"My philosophy on doing political ads is you've got to get people to listen and then if (they listen), they understand. It's really about big oil trying to buy this seat," Cloud said.

Contributors to Californians for Jobs and a Strong Economy include Union Pacific Railroad and Tejon Ranch Company, which donated $5,000 each and PG&E Corp., which gave $3,000.

Occidental Oil and Gas Corp., which had a contentious battle with farming interests before the Kern County Board of Supervisors, gave the PAC $25,000.

But Chevron was, by far, the biggest contributor, according to the group's campaign finance reports, giving $100,000 in April.

Perez was given $4,100 by the group for the primary race.

Californians for Jobs spent $227,093 in May -- much of it on television -- to support Perez. Since then it hasn't made any contributions, or paid a dime in support of Perez.

Chevron has contributed another $150,000 to Californians for Jobs -- bringing its total contributions to $250,000.