Forty American billionaires have pledged to give at least half of their fortunes to charity as part of a campaign by Bill Gates and Warren Buffett.
Microsoft founder Gates and investor Buffett, who are worth a combined $90bn (£56.6bn), have persuaded 38 of their fellow billionaires to sign up.
The friends and philanthropists started The Giving Pledge last month.
Its aim is to persuade fellow billionaires to pledge the money to charity, either in their lifetime or after they die.
Buffett said: “We’ve really just started, but already we’ve had a terrific response.
“At its core, the Giving Pledge is about asking wealthy families to have important conversations about their wealth and how it will be used.”
He added: “We’re delighted that so many people are doing just that – and that so many have decided to not only take this pledge but also to commit to sums far greater than the 50% minimum level.”
Those who sign the pledge are also invited to publish a letter explaining their decision.
Among the latest batch to have signed up is New York Mayor Michael Bloomberg, who is worth $18bn (£11.3bn).
In his letter Bloomberg wrote: “Making a difference in people’s lives – and seeing it with your own eyes – is perhaps the most satisfying thing you’ll ever do. If you want to fully enjoy life – give.
“And if you want to do something for your children and show how much you love them, the single best thing – by far – is to support organisations that will create a better world for them and their children.”
Joining him is Star Wars Director George Lucas.
Lucas wrote: “My pledge is to the process; as long as I have the resources at my disposal, I will seek to raise the bar for future generations of students of all ages.”
Others on the list include entertainment executive Barry Diller ($1.2bn, £775m), Oracle co-founder Larry Ellison ($28bn, £17.6bn), energy tycoon T. Boone Pickens ($1.1bn, £692m), media mogul Ted Turner ($4.8bn, £3bn), banker David Rockefeller ($2.2bn, £1.3bn) and investor Ronald Perelman ($11bn, £6.9bn).
They join Eli Broad, who made his money in property, venture capitalist John Doerr, media entrepreneur Gerry Lenfest and former Cisco Systems Chairman John Morgridge in supporting the effort.
The US has 403 billionaires, the most of any country, and all together they have a combined fortune of $1.3 trillion.
Mr Buffett himself pledged to give 99% of his wealth to good causes in 2006.
Gates and Buffet will now wine and dine other billionaires in an attempt to persuade them to follow suit.
The Sky