MIG-31

Independent developer Valve has released lifetime retail sales figures for most of its own titles released over the company's ten-year history, partially quantifying the company's ongoing success by demonstrating tens of millions of units sold.

But Valve kept some cards close to the chest, declining to reveal digital download numbers. (All of the following statistics were described as Valve's estimates of worldwide lifetime-to-date retail sales.)
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Source: Gamasutra

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