Privately-held Valve Corporation is tight-lipped about revenues, and Newell doesn't comment on his personal finances. So in order to estimate his net worth, Forbes consulted with video game industry insiders, equity analysts, investment bankers, and technology analysts to figure out what the company is worth. Even the most conservative estimates put Valve's enterprise value at more than $3 billion, and since Newell owns more than 50% of the company, that means he's worth at least $1.5 billion.