Billionaire Oracle founder Larry Ellison will join film director George Lucas and 38 other mega-wealthy people in following a call by Warren Buffett and Bill and Melinda Gates to pledge to give the majority of their riches to charity.

On Wednesday, Buffett announced that 40 of America's wealthiest individuals and families, from former Citigroup leader Sandy Weill to hotel mogul Barron Hilton, have signed the "Giving Pledge".