The statistics were published in the latest issue of US games magazine Game Informer and only cover sales made through traditional retail, rather than the firm’s digital distribution service, Steam.
The original Half-Life has sold 9.3 million copies to date, with its spin-offs Opposing Force and Blue Shift selling 1.1 million and 800,000 respectively. The sequel, Half-Life 2 sold 6.5 million, with a further 1.4 million sales for its expansion, Half-Life 2: Episode One.
The Orange Box, which contains Half-Life 2, Episodes One and Two, Team Fortress 2 and the critically acclaimed Portal, has sold 3 million copies worldwide. Combined sales for the online multiplayer series Counter Strike, encompassing the original version, Condition Zero, Source and the Xbox port, has sold 10.7 million copies.
Finally, Left 4 Dead is projected to sell between 3.6 million and 3.9 million. If excluded from Valve’s total, the publisher has managed to shift 32.8 million copies of its games over the past ten years. Taking the estimated Left 4 Dead figures into account, the company boasts sales of between 36.4 million and 36.7 million units.