HARRISBURG — Republican gubernatorial nominee Tom Corbett is the biggest beneficiary of a surge in campaign contributions from the natural-gas industry, which has a huge stake in a proposed new tax that has emerged as a major campaign issue, a watchdog organization said Thursday.

Corbett, the state attorney general and front-runner in the governor's race, received $357,775 from industry political committees and executives between Jan 1. and Sept. 13, according to MarcellusMoney.org, a project of the Conservation Voters of Pennsylvania and Pennsylvania Common Cause. His Democratic rival, Dan Onorato, received $62,000 from the industry, the groups said.

Onorato, the elected chief executive of Allegheny County, advocates a tax to generate money for environmental protection as drilling on the gas-rich Marcellus Shale reserve intensifies across the state. Corbett opposes any new levy, saying it could hurt the industry.

During the 97-day period covered by the latest campaign finance reports, Corbett's campaign received $334,500 from the natural-gas industry, the groups said. That is about 5 percent of the $6.1 million he received from all donors during that period.

Onorato received $45,000 during that period, the groups said — about 1 percent of the nearly $5 million he raised.

A campaign spokesman said Corbett's superior fundraising shows that his contributors support his agenda for lower taxes, less spending and smaller government.

"Corbett is for jobs, Onorato is for taxes," Kevin Harley said.

Onorato campaign spokesman Brian Herman said Corbett "clearly wants to protect the industry because the industry is doing a lot to help him."

"Unfortunately, the taxpayers are going to suffer," he said.

Pennsylvania is the only major gas-producing state that doesn't tax drilling.

Leaders of the GOP majority in the state Senate support a severance tax, as does Democratic Gov. Ed Rendell, who is stepping down in January after serving the maximum two terms. Efforts to negotiate a compromise on the tax rate were continuing Thursday but major issues remained unresolved.