NEW YORK, USA: Thirty-four U.S. billionaires pledged on Wednesday to give away at least 50 per cent of their wealth to charity as part of a campaign by investor Warren Buffett and Microsoft founder Bill Gates.

Among the billionaires joining the campaign are New York Mayor Michael Bloomberg, entertainment executive Barry Diller, Oracle co-founder Larry Ellison, energy tycoon T. Boone Pickens, media mogul Ted Turner, David Rockefeller and investor Ronald Perelman.

Gates and Buffett launched "The Giving Pledge" in June to convince hundreds of U.S. billionaires to give away most of their fortune during their lifetime or after their death and to publicly state their intention with a letter of explanation.

This commitments bring to 40 the number of billionaires giving away half their wealth. Many of those listed have already been engaged in significant philanthropic efforts. Below are details on how much they are worth, based on data from Forbes magazine, and how they made their fortune.

Bill and Melinda Gates – founder of software giant Microsoft and the Bill and Melinda Gates Foundation; worth $53.5 billion.

Warren Buffett – famed investor who made his fortune through his Berkshire Hathaway firm, which buys companies he sees as undervalued; worth $47 billion.

Eli Broad – the real estate and construction billionaire founded home builder Kaufman & Broad, worth $5.7 billion; has already given more than $2 billion to The Broad Foundations; worth $5.9 billion.

John Doerr – venture capitalist with Kleiner Perkins Caufield & Byers who made millions with early bets on Amazon, Netscape and Sun Microsystems and became a billionaire with Google; worth $1.7 billion.

Gerry Lenfest – the media entrepreneur has already given away more than $800 million, or about 65 per cent of his fortune, a spokeswoman said.

John Morgridge – Former Cisco Systems chairman now focuses on philanthropy; worth $1.6 billion.

Paul Allen – Founded software giant Microsoft with Gates; worth $13.5 billion.

Laura and John Arnold – John Arnold worked as a high-flying trader at Enron and then founded hedge fund Centaurus Energy; worth $4 billion.

Michael Bloomberg – the mayor of New York City made his fortune by founding the news and information company which bears his name, Bloomberg LP; worth $18 billion.

Michele Chan and Patrick Soon-Shiong -- Patrick is the son of a village doctor in China who made his fortune on cancer treatments and generic drugs; worth $5 billion.

Barry Diller and Diane von Furstenberg – Diller made his fortune on the Home Shopping Network while wife von Furstenberg is a renowned fashion designer; worth $1.2 billion.

Larry Ellison – founder of database giant Oracle; worth $28 billion.

Barron Hilton – Son of hotel legend Conrad Hilton who built his father's hotel empire; worth $2.5 billion.

Jon and Karen Huntsman – Jon is worth $1 billion, made by turning Huntsman Corp from a fast-food container supplier into America's largest private chemical company.

Joan and Irwin Jacobs – Founded Qualcomm, which commercialized CDMA digital wireless technology; worth $1.2 billion.

George Kaiser – His Kaiser-Francis Oil is among the world's biggest private energy producers and owns $2 billion stake in Bank of Oklahoma; worth $10 billion.

Elaine and Ken Langone – Ken is an investment banker who took Ross Perot's Electronic Data Systems public in 1968 and was an early investor in Home Depot; worth $1 billion.