Three founders of Facebook are the top three wealthiest technology entrepreneurs under the age of 31, according to Wealth-X.

Mark Zuckerberg, 29, co-founder, CEO and chairman of Facebook, is the richest technology entrepreneur with $17.3 billion. Zuckerberg’s wealth increased by $3.7 billion in July when the price of Facebook shares soared because of mobile advertising revenue, according to Wealth-X, a research firm that focuses on ultra-high-net-worth individuals and families.

Facebook co-founder Dustin Moskovitz, 29, who is now CEO of Asana, an online tool for business team management, is second with $4.2 billion.

Chris Hughes, 29, co-founder, who is now publisher and editor-in-chief of New Republic, is third with $950 million.

Fourth on the list is Andrew Houston, 30, with $610 million. He is co-founder and CEO of Dropbox, an online data-sharing service.

Nathan Blecharczyk, 30, completes the top five list with $500 million. He is chief technology officer for Airbnb, an online service for vacation housing rentals.