The newest members of the club include Netflix chief executive Reed Hastings, Intel co-founder Gordon Moore, and Charles Bronfman, the Canadian-born former head of Seagram Co.

The Giving Pledge, announced in 2010, is was launched by Microsoft mogul Gates and investment guru Buffett who want to convince the richest people in the country to give 50 percent or more of their fortune to charity.

The group includes CNN founder Ted Turner, New York Mayor Michael Bloomberg, Oracle co-founder Larry Ellison and Hollywood director George Lucas, as well as Buffett and Gates.

"We've said from the beginning that this is a long-term effort, so it's exciting to see continued progress over the last two years," said Gates, who is co-chair of the Bill and Melinda Gates Foundation.

"This new group brings extensive business and philanthropic experience that will enrich the conversation about how to make philanthropy as impactful as possible.

Their thoughtfulness and deep commitment to philanthropy are an inspiration to me, and I'm sure to many others as well."

The newest members also include Manoj Bhargava, India-born founder of 5-hour Energy; and Dan Gilbert, founder and chairman of Quicken Loans and majority owner of the Cleveland Cavaliers.

Also pledging were Peter Lewis, chairman of Progressive Insurance; Jonathan Nelson, founder of Providence Equity Partners; Jorge Perez, chairman and CEO of The Related Group; Albert Lee Ueltschi, founder of FlightSafety International; and Symphony Technology Group founder Romesh Wadhwani.

New pledges also came from Claire Tow, co-founder one of a major cable

television company, and husband Leonard Tow, the CEO of New Century Holdings.