One of the world's richest men, Adelson is donating $10 million to the campaign activities of billionaire brothers Charles and David Koch. A person familiar with Adelson's pledge confirmed the donation Friday but requested anonymity to discuss the private arrangement.
Adelson has already contributed $10 million to a super political action committee that backs likely Republican presidential candidate Mitt Romney, Restore Our Future, and $5 million to each of two organizations promoting House Republicans.
During the GOP presidential primary, Adelson and members of his family gave $21 million to a super PAC promoting former House Speaker Newt Gingrich.
Top executives of Wichita, Kan.-based Koch Industries Inc., Charles and David Koch founded the small-government, anti-tax group Americans for Prosperity. They are nationally recognized for supporting conservative causes and candidates.
Koch Industries has more than 60,000 employees worldwide and $110 billion in annual revenues, with interests that include oil refineries, fertilizer, chemicals, paper and pollution-control equipment.
The Supreme Court's Citizens United decision in 2010 and other federal rulings ended restrictions on political contributions from corporations, labor unions and millionaires and billionaires. The Obama campaign has said he could become the first incumbent president to be outspent by his opponent and his opponent's supporters.