George Soros, Paul Allen, Michael Bloomberg Top List Of Philanthropists In 2011 (SLIDESHOW)

The top 50 donors in the U.S. gave $10.4-billion last year, up from $3.3 billion the previous year, according to the Chronicle of Philanthropy.

One large gift -- $6 billion from heiress Margaret A. Cargill -- boosted the numbers. Excluding her donation, major gifts totaled $4.4 billion.

A recently released study from PNC Wealth Management reveals that 59 percent of millionaires feel they have an obligation to give back to their community.

"It is encouraging to see that millionaires, considering today's economic headwinds, recognize a personal responsibility to give back to perpetuate the legacy of a 'cared for society,'" R. Bruce Bickel, senior vice president of PNC Wealth Management, said in the release.

Eli Broad, billionaire real-estate titan who founded the Broad Foundation to improve urban education, attributes the increase in giving to economic trends, according to the Chronicle report.

“Consumer confidence is up, business confidence is up modestly,” says Eli Broad who last year gave $27-million to his foundations. “If that continues, people will open their purses wider.”

Warren E. Buffett, Bill and Melinda Gates and Ted Turner are not on the list as they are paying off pledges made in previous years and not making new commitments, the Chronicle reports.

Mark Zuckerberg is absent from the Top 50 list this year. He came in No. 10 last year after giving $100 million to New Jersey schools.

Charitable giving in general rose 7.5 percent in 2011, compared to 2010, the Atlas of Giving reported.

Check out the full list of the Philanthropy 50 at the Chronicle of Philanthropy.

SLIDESHOW: Top 10 Philanthropists Of 2011