Steam saw an increase in game sales revenue of $800 million in 2017 over the year prior, according to Sergey Galyonkin of SteamSpy.
Based on Golyonkin's estimates, revenue generated from sales peaked at $4.3 billion last year, up from $3.5 billion in 2016, making it a record-breaking year for Valve.
Speaking at GDC yesterday, Galyonkin revealed that around half of that $4.3 billion was generated by just 100 of the 21,000 games available on Steam. In other words, 0.5% of games accounted for 50% of sales revenue.
Topping the list of highest earners was PlayerUnknown's Battlegrounds generating $600 million with 28 million owners on Steam.
In second-place was Counter-Strike: Global Offensive with $120 million, and Grand Theft Auto V with $83 million. Of the top 20 games, seven were released before 2017, including Civilisation VI, The Witcher III: Wild Hunt, Rainbow Six Siege, Dark Souls III, and Rocket League.
Along with obvious money spinners such as Call of Duty: World War II - which came in at fourth with $41 million generated in sales from 840,000 copies owned - were more surprising entries such as Cuphead at 20 with 1.3 million owners and a sales revenue of $22 million.
It's worth noting that the data is not completely flawless however as it does not include microtransactions, DLC, or in-app purchases. As a result, free-to-play games and titles with additional in-game monetisation are underrepresented.