Washington, Aug 5 (IANS): Forty billionaires and their families in the US have pledged to donate more than half of their fortune to charity.

The donators include Microsoft founder Bill Gates, businessman Warren Buffett, Microsoft co-founder Paul Allen, New York Mayor Michael Bloomberg, pharmaceutical tycoon Patrick Soon-Shiong, Oracle founder Larry Ellison and Hollywood director George Lucas, Xinhua reported.

The list also include David Rockefeller, from the Rockefeller family, and Barron Hilton, son of Hilton Hotels founder Conrad Hilton.

The families all participated Wednesday in the "Giving Pledge", a donation drive launched by Buffett and Gates. The idea was to invite the wealthiest individuals and families in the US to give the majority of their wealth for philanthropic causes and to charitable organisations during their lifetime or even after their death.

"The pledge is a moral commitment to give, not a legal contract," a statement from the Giving Pledge said.

Buffett said the drive has "just started, but already we've had a terrific response".