WASHINGTON -- Just two dozen ultra-wealthy donors are behind a surge of million-dollar contributions to the new breed of political committees during the presidential campaign.

Millionaire and billionaire executives have unlocked their personal vaults to write seven-figure checks to support the campaigns of Democratic President Barack Obama and the Republicans vying to oppose him: Mitt Romney, Rick Santorum, Newt Gingrich and Ron Paul.

More than half of the $60 million collected so far by the new group of independently run super political action committees came from just 24 wealthy Americans, according to an Associated Press review of financial reports filed by the campaigns. The super-sized checks amount to $33 million and, in some cases, the contributions of $1 million or more represent most of the money that several super PACs have collected.

These outsized donations, more than 40 times the amount ordinary Americans can give directly to a politician, are allowed under the landmark 2010 Supreme Court ruling in the Citizens United case. The ruling made it possible for super PACs to raise and spend unlimited sums to support political campaigns.

Some of the wealthiest donors:

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Nobody approaches the $11 million that Las Vegas casino billionaire Sheldon Adelson and his family have given to Winning Our Future, the group supporting Gingrich, which has $13.1 million in total contributions.

The co-founder of PayPal and an early investor in Facebook, Peter Thiel, has given $2.6 million to Endorse Liberty, supporting Paul.

The chief executive at DreamWorks Animation, Jeffrey Katzenberg, has given $2 million to the group supporting Obama's re-election, Priorities USA Action, which accounts for nearly half the group's $4.5-million total.

Hotel magnates Bill and Richard Marriott have given $1.5 million to Restore Our Future, the group supporting Romney.

The Red, White and Blue Fund, backing Santorum, collected much of its $2.8 million from $1-million donors. One was from mutual fund entrepreneur Foster S. Friess, a funder of the conservative Web news aggregator Daily Caller.