"According to the firm, Steam alone had an estimated revenue of $970 million USD in 2010. Its biggest-selling game for the year was Activision's Call of Duty: Black Ops for $98.2 million followed by Call of Duty: Modern Warfare 2 for $39.4 million. Its third largest selling game for the year was Valve's own Left 4 Dead 2 which raked in an impressive $36 million. Steam even took in an estimated $213 million in December alone, probably due to its crazy year-end holiday sale."