HELENA, Mont. — Republican gubernatorial candidate Greg Gianforte continues to pour his own money into his bid to unseat Montana Gov. Steve Bullock, donating another $1.5 million to his campaign last month, according to campaign finance reports filed Monday.

The Bozeman businessman, who sold RightNow Technologies to Oracle in 2011 for $1.8 billion, has now donated more than $3.1 million of his personal wealth to the campaign, stretching back to the primaries.

“I know of no other candidate that has self-invested this much in a (Montana) governor’s race,” Montana State University political science professor David Parker said.

Gianforte’s campaign is pumping most of that money into television ads, spending $1.36 million in media buys between the end of August and the end of September. That represents most of Gianforte’s $1.77 million in total spending for the period, which left him with about $224,000 at the end of September.

Bullock spent less than a third of what Gianforte did on ad buys last month, according to the Democrat’s campaign finance report.

“It appears to be creating a large informational asymmetry on the airwaves, which creates a possible advantage for (Gianforte) in the final days of the campaign,” Parker said.

However, former U.S. Rep. Denny Rehberg also had the airwave advantage over incumbent U.S. Sen. Jon Tester in 2012, but he still lost to Tester, Parker added.

Outside groups are also clogging the airwaves with ads in support of their candidates, with the Democratic Governors Association-funded Good Jobs Montana political committee spending $1 million on ads against Gianforte last month.

The Republican Governor’s Association Right Direction PAC spent $730,000 over that period on ads opposing Bullock.

Carroll College political science professor Jeremy Johnson said that because the Montana media market is cheap, both candidates have enough money to get their messages out.

However, too many ads could backfire, he said. “It is important to have sufficient funds for campaigns to reach voters; however, there are rapidly diminishing returns to ad buys when the airwaves are saturated with competing commercials,” Johnson said.

Bullock’s campaign pounced on Gianforte’s latest campaign finance report, repeating its past claim that Gianforte is trying to buy the election. Gianforte’s campaign chose not to address the candidate’s self-funding, instead highlighting that he took in $226,589 in donations for the period.

Bullock raised nearly $282,000 last month, and he took in large PAC contributions from unions, BNSF Railway, the financial firm Deloitte and the drug company Pfizer.

Bullock spent $538,280 and had more than $1 million to spend going into the final month of campaigning.