The two founders remain neck and neck on Bloomberg Billionaires Index on Thursday, both worth an estimated $81.6 billion, with Zuckerberg's Facebook fortune rising and Buffett's net worth falling. (The daily ranking of billionaire net worth is updated at the end of the trading day in New York.)
The gap between the two men's net worth was only $29 million as of Wednesday, according to Bloomberg. That day, Facebook shares rose 2.3 percent, landing Zuckerberg an extra $1.7 billion, according to Forbes.
Currently the fourth richest person in the world, Zuckerberg's net worth is the highest it has ever been, according to Bloomberg's tracking, which goes back to 2012 when Facebook went public.
Ninety-eight percent of Zuckerberg's wealth is in Facebook stock, according to an analysis by WealthX. He also owns a house estimated to be worth $9 million in Palo Alto, California, and land in Hawaii estimated to be worth $100 million, as well as liquid assets.
Facebook's stock price was trading up above $200 Thursday as of 1 p.m. EST.