Musk owns 20.8% of Tesla's stock, making his stake worth just under $60 billion.
Musk is also the primary shareholder of privately held SpaceX, as well as a privately held tunneling company.
Buffett's fortune fell this week after he donated nearly $3 billion worth of Berkshire Hathaway stock to charity — part of his plan to give away most of his wealth to philanthropic ventures.
Tesla's stock is up more than 500%Â over the past 12 months, exceeding the value of almost every company in the S&P 500.