(CNN) — Thanks to $10 million in new donations from Nevada billionaire Sheldon Adelson and his wife, the pro-Romney super PAC Restore Our Future raised more than $20 million during the first half of this month, according to a financial disclosure form filed with the Federal Election Commission Thursday.

The group had more than $36 million cash on hand, and spent $12 million, as of October 17.

The haul so far in October is almost as much as it raised in August and September combined.

The new contributions by the Adelsons bring the couple's total to Restore Our Future to $20 million.

Restore Our Future launched a major swing state ad campaign earlier this week, buying almost $18 million worth of commercial time in 10 states.

For the Adelsons, who rank as the top givers to outside political groups according to the non-partisan Center for Responsive Politics, this latest donation means they have given at least $61 million this campaign cycle to entities which have to disclose their donors: super PACs, campaign committees and candidates.

Mr. Adelson is a controversial Nevada magnate who operates casinos both in Nevada and overseas.

He has been the highest profile Republican donor this election cycle because of the growing influence of super PACs and his willingness to give to them. He and his wife donated millions to Winning Our Future, the super PAC that was largely responsible for helping keep Newt Gingrich in the GOP primary contest.

After Gingrich dropped out, Adelson was at first reluctant to support Romney. After several meetings and conversations, however, Adelson decided to embrace the Republican nominee. One reason, associates have said, is because Adelson is determined to do all he can to make sure President Barack Obama is not re-elected. Another key objective for him is the safety of Israel, and he believes Romney would be a stronger friend of the Jewish state than Obama, friends have said.

Adelson hosted a fund-raiser for Romney and went to Israel to join the Republican nominee during his July trip.

He has told friends he and his wife could spend as much as $100 million this election to help elect the Republican nominee and support GOP congressional candidates.

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By Kevin Bohn

CNN Senior Producer