Valve has always been tight-lipped with their sales numbers, especially when it comes to sales made over Steam, but they released a ton of numbers today.
The numbers show the lifetime sales at retail for most of their first-party games, but do not include sales on Steam. That remains a mystery and a closely guarded secret, but it's safe to assume that Steam is wildly successful with the amount of companies flocking to the service.
Hit the jump for the numbers.
Half-Life - 9.3 million
Half-Life: Opposing Force - 1.1 million
Half-Life: Blue Shift - 800,000
Counter-Strike - 4.2 million
Counter-Strike: Condition Zero - 2.9 million
Counter-Strike: Source - 2.1 million
Counter-Strike (Xbox) - 1.5 million
Half-Life 2 - 6.5 million
Half-Life 2: Episode One - 1.4 million
The Orange Box - 3 million
Left 4 Dead - Estimated 3.6 - 3.9 million
All in all, that's over 35 million units sold at retail. That doesn't even include numbers sold on Steam. Personally, I've purchased every single Valve game released (yes even Condition Zero...) and have done so on Steam since they started the service.
What about you? Which games have you purchased and how many of them were bought in a store vs. Steam?