Vermont Sen. Bernie Sanders racked up nearly $300,000 on airfare in October as he flew around the country in the final weeks of the campaign.

His spending on private jet travel took him to nine states to boost Democrats in the elections, although some of his efforts took him to key presidential primary states.

Among those was a trip to Columbia, S.C., to campaign for Democrat James Smith, who was defeated in his bid for governor. He also campaigned in Iowa and other states.

The spending by the campaign, Friends of Bernie Sanders, was revealed on campaign finance reports as a contribution to Apollo jets, local site VtDigger.com reported.

Sen. Bernie Sanders (I-VT) speaks during a rally for Nevada Democratic candidates at the Las Vegas Academy of the Arts on October 25, 2018 in Las Vegas. His

'This cost covered the entirety of the tour from Indiana, Michigan, Wisconsin, Iowa, South Carolina, Colorado, Nevada, Arizona, California, and back to Vermont,' Sanders spokeswoman Arianna Jones told the publication.

Sanders also flew to Florida in October to campaign for candidate for governor Andrew Gillum.

Sanders also traveled to Iowa, where he backed J.D. Sholten in his effort to topple Republican Steve King, who nevertheless won reelection.

Sanders' hefty air fare tab came at a time he was calling climate change the greatest threat to the planet.

However, his campaign says he purchases carbon offsets.

Sanders' campaign says it purchased carbon offsets for the flights

AKRON, OH - MARCH 14: Democratic presidential candidate Bernie Sanders boards his campaign plane after a rally at the Akron Civic Theatre on March 14, 2016 in Akron, OH

'Climate change is the single greatest threat facing our planet. On Nov 6th, we must show up at the polls from coast to coast and stand with candidates who are willing and ready to accelerate our transition to clean energy, and finally put people before the profits of polluters,' Sanders tweeted Oct. 17.

'The campaign purchased carbon offsets from NativeEnergy to support renewable energy projects and invest in carbon reduction projects to balance out the emissions produced on the trip,' Jones told The Daily Caller News Foundation.

Sanders' advisor, Jeff Weaver, told the Associated Press this week that if Sanders decides to run for president again, he will have 'a much bigger campaign' if he runs in 2020.