The Giving Pledge effort led by billionaires Warren Buffett and Bill Gates added 17 individuals and families to the cause this week, bringing to 154 the number of signatories vowing to donate the majority of their wealth to charity.

Added pledgers include investor HRH Prince Alwaleed bin Talal, the wealthiest of the new group with a $19.8 billion fortune, according to the Bloomberg Billionaires Index, and the first from Saudi Arabia.

Also joining are Airbnb's Brian Chesky, Joe Gebbia, Nathan Blecharczyk and his wife Elizabeth, marking the first time co-founders of a company signed on at once, according to the Giving Pledge's statement Wednesday. Salesforce founder Marc Benioff and his wife Lynne joined the pledge, as well as Mengniu Dairy founder Gensheng Niu, the first from mainland China.

"This new group joining the Giving Pledge is incredibly thoughtful about their desire to give back and help solve the world's toughest challenges through philanthropy," Gates said in the statement.

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"Some have been giving for decades and others are just starting out after building successful businesses, but they all see the value of giving in a bold and effective way. Melinda, Warren and I are glad to have the opportunity to learn with them and from them."

The Giving Pledge was founded in 2010 by Buffett, Gates and his wife and Melinda Gates, the co-founder of Microsoft has a fortune of $85.5 billion, making him the richest person on Bloomberg's index. Together with Buffett they're worth a combined US$151.8 billion (NZ$222 billion).

The new group of donors follows in the footsteps of Mark Zuckerberg and his wife who last year committed to give away virtually all of their US$46 billion (NZ$67 billion) in Facebook shares.

In all, Giving Pledge signatories hail from 16 countries and range in age from 30 to 100.

The group completed its annual learning conference this week, where they discussed opportunities for women in the global economy, environmental issues, urban renewal and philanthropy's role in advancing scientific discovery.

Public disclosures of lifetime and estate giving of deceased billionaires who signed the pledge show that fulfillment varies widely, Bloomberg News reported last year.

Signatories are under no legal obligation to donate any of their money, and sometimes fail to give away anywhere close to half. Charity regulations and estate law can block public disclosures.