RICHMOND -- Democrat Mark Warner holds an enormous funding advantage over Republican Jim Gilmore in their race for a seat in the U.S. Senate, according to financial reports the campaigns filed Tuesday.

Warner ended June with $5.1 million in the bank and had spent about three and a half times as much money as Gilmore had raised for his entire campaign. Gilmore, who barely survived a convention fight for the GOP nomination, had less than $117,000 in available cash at the end of the month.

The former governors are seeking the seat held by Republican John Warner, who will retire after serving 30 years in the Senate. The two Warners are not related.

Mark Warner has raised a total of about $9.3 million for his Senate campaign, while Gilmore has raised about $1.2 million, according to reports filed with the Federal Elections Commission.

The funding gap could raise questions about Gilmore's ability to compete with Warner, who also leads in early public opinion polls.

"How does he [Gilmore] get through the race?" said Larry Sabato, the director of the University if Virginia Center for Politics. "It's a legitimate question."

Warner managed to expand an already sizable financial advantage over the past three months despite spending more than $1 million on an initial round of television advertising in June.

Warner's campaign said that more than 81 percent of its individual donors between April 1 and June 30 were Virginians.

"We are grateful that so many Virginians are actively supporting Governor Warner's campaign to take his record of honest, common-sense results to Washington," Warner spokesman Kevin Hall said.

Gilmore, who preceded Warner as governor, raised about $480,000 during the same three months, a period in which he had to fend off a nomination challenge from Del. Bob Marshall of Prince William County.

Gilmore spokeswoman Ana Gamonal said the campaign has benefited largely from small-dollar donors as Gilmore aimed his campaign message at "working families." More than 3,800 of the campaign's individual donors have contributed less than $200, she said.

"We're focused on raising what we need to get our message out," Gamonal said.

Warner released his second television ad of the campaign Tuesday. The 30-second spot, which highlights Warner's energy agenda, is airing in Roanoke and four other Virginia markets.

The ad notes Warner's support for advancing alternative energy sources and cracking down on oil speculators. It also mentions the Democrat's support for expanding domestic oil and gas production and shows footage of an offshore drilling platform.

Gilmore's campaign pounced on the ad, saying it muddies Warner's position on domestic oil production. Gilmore favors drilling for oil off the coast and in Alaska's Arctic National Wildlife Refuge. Warner opposes drilling in the Alaskan wilderness, but would support offshore drilling if approved by coastal states, Hall said.

Gamonal said Warner is sending mixed signals about his support for offshore drilling. She insisted Gilmore is more committed to increasing domestic oil production in an effort to ease pressure on gas prices.

The issue is certain to surface Saturday when the two candidates have their first debate of the campaign. Warner and Gilmore will go head-to-head at The Homestead resort in Bath County in an event sponsored by the Virginia Bar Association.

"Governor Warner is anxious to discuss his record of accomplishment and his bipartisan approach to getting things done and putting forward his positive vision," Hall said of the debate.

Gilmore said the debate provides a chance "to smoke him [Warner] out on some of the issues."

"It's finally, hopefully a chance to hear some substance from Mark Warner on what his positions are on national and federal issues," Gamonal said.