> Not that Mr. Newell hasn’t had opportunities to sell out. Valve has been pursued over the years by Electronic Arts, which would very likely have valued Valve at well over $1 billion had the talks progressed that far, said two people with knowledge of the discussion who spoke on condition of anonymity because the talks were private.

> Although Valve’s finances are private, Michael Pachter, an analyst at Wedbush Securities, estimates that the company could be worth around $2.5 billion today.

It's guesswork and no method is explained though, so it's not like that's a very reliable estimate or anything.