Sales from Valve's digital distribution client are not factored in, with the figures only accounting for worldwide retail sales. With Half-Life 2, Valve began simultaneously releasing all of its PC games at retail and via Steam. The numbers were originally printed in the November issue of Game Informer, then republished by Gamasutra.
Furthermore, it was not specified if the figures of multiplatform games--Half-Life, Half-Life 2, The Orange Box--included both PC and console sales, or just PC.
- Half-Life (Valve) / 1998 - 9.3 Million
- Half-Life: Opposing Force (PC, Gearbox) / 1999 - 1.1 Million
- Half-Life: Blue Shift (PC, Gearbox) / 2001 - 800,000
- Counter-Strike (PC, Valve) / 2000 - 4.2 Million
- Counter-Strike: Condition Zero (PC, Valve) / 2004 - 2.9 Million
- Counter Strike: Source (PC, Valve) / 2006 - 2.1 Million
- Counter-Strike (Xbox, Valve) / 2003 - 1.5 Million
- Half-Life 2 (Valve) / 2004 - 6.5 Million
- Half-Life 2: Episode One (PC, Valve) / 2006 - 1.4 Million
- The Orange Box (Valve) / 2007 - 3 Million
(Half-Life 2 HL2: Episode One, HL2: Episode Two, Portal, Team Fortress 2)