Elon Musk, Jeff Bezos, and Mark Zuckerberg make up around a fifth of the collective fortune of all of America’s billionaires, thanks to their early innovation in social media, fintech, and e-commerce.

Musk, the richest person in the world with an estimated net worth of $374 billion per Bloomberg’s Billionaire Index, is known for his lucrative ventures, including PayPal, Tesla, and SpaceX. Meta CEO Zuckerberg accumulated $259 billion thanks to the success of his social platform, Facebook. And Bezos earned his billionaire status after founding Amazon from his garage in Bellevue, Washington—a retail giant now worth $2.39 trillion. 

But despite these Silicon Valley titans holding most of America’s wealth, the majority of U.S. billionaires made their fortunes in banking and finance—including Berkshire Hathaway’s Warren Buffett, Fidelity’s Abigail Johnson, and Blackstone’s Steve Schwarzman. 

Around 110 of the 1,135 ultra-wealthy got rich in technology, and 75 made their money in real estate. 

As billionaires accumulate more wealth—AI could create the world’s first trillionaires and worsen the class divide—there’s an opportunity for ground-breaking philanthropic giving. But few are actively paying it forward, even those that pledge to do so.

Billionaires have donated or pledged around $185 billion over the past decade—just 3.25% of their wealth

In 2010, Buffett, Bill Gates, and Melinda French Gates created The Giving Pledge: a philanthropic campaign where billionaires publicly commit to give away at least 50% of their fortunes to charity in their lifetimes or wills. 

However, in reality, only nine of the 256 signers have successfully followed through on the promise over the last 15 years. 

If anything, many are only getting richer; the net worth of the original 57 U.S. signers has increased by 283% since signing, or 166% adjusted for inflation. And only about a quarter of The Giving Pledge signatories have known donations of less than $1 million in the last 10 years, according to the Altrata data. 

In total, billionaires have publicly donated or pledged to give around $185 billion over the past decade—only about 3.25% of the $5.7 trillion stash. According to Altrata, they’ve donated about $90 billion to educational or medical causes specifically since 2015. 

A more private way to donate: billionaire foundations

Another popular method of philanthropic spending is through personal foundations. Many billionaires including—Bill Ackman and Gates—have their own foundations where they serve as trustees. Ackman, the founder and CEO of Pershing Square Capital Management, has given about $1.36 billion of his $8.31 billion fortune to his charitable organization that he runs with his wife, according to Altrata. 

Meanwhile Gates is all-in his Gates Foundation’s mission that he formed with his ex-wife Melinda. This July $51 billion was wiped from his fortune, shooting him down the billionaire list from fifth place to 12th because he gave so much away.

Mackenzie Scott, an early employee at Amazon and the ex-wife of Bezos, has given away over $19.25 billion to date across 2,450 nonprofits through her Yield Giving foundation. Her giving methodology often entails donating anonymously directly to nonprofits, trusting them to handle the funds as they see fit, with no expectations. 

Experts told Fortune the uber-rich could be inspired by her actions to contribute directly to organizations and ease the tax hit. The mega philanthropist signed The Giving Pledge in 2019. 

“I think she’s a trendsetter and sort of moral ballast to the way that Gates has been,” Bella DeVaan, associate director of the charity reform initiative at the Institute for Policy Studies, previously told Fortune. “I do see that being not just a trend, but shifting common sense toward trust-based philanthropy.”