For years, Valve has been an impenetrable fortress when it came to data. Number of sales, amount of hours played, most-played games—all locked up behind a Fort Knox-like wall. Interested parties were forced to rely on the benevolence of developers for info, like when The Stanley Parable sold 100,000 copies in three days.
But last night, Ars Technica revealed that Steam’s Fort Knox is only so impregnable from the front. Go around to the side, and there’s a huge tunnel replete with neon signs that said “Welcome!” and “Come on in!” So they did.
Ars Technica’s custom “Steam Gauge” tool essentially functions like a search engine—it crawls individual profile pages and scrapes info on what games are owned, how long each game has been played, et cetera. The crawler can only cover 0.04 percent of Steam profiles per day, but through the power of statistics and random sampling Steam Gauge’s three-day rolling total provides a pretty good look at Steam as a whole service. If you’re curious about more of the science behind Steam Gauge, you can read Kyle Orland’s incredibly excellent original article.

Dota 2 is the most-owned game on Steam, with over 25 million players.
So what insights can Orland’s Steam Gauge share? The first report alone reveals several fascinating tidbits.
Despite Steam’s presence as the most well-known PC games retailer, most people still primarily own Valve’s games. The ten most-owned games on Steam are all Valve’s, with the list dominated by Dota 2 (25 million owners) and Team Fortress 2 (20 million). Of course, Dota 2 and Team Fortress 2 are both free-to-play, so no surprise the adoption rates are so high there.
The rest of Valve’s games? Well, they’re not played nearly as much as they’re owned, likely because Valve sometimes gives its games away for free. Organize games by “Most Played” and a lot of Valve’s titles fall right off the list, to be replaced by other games like Elder Scrolls V: Skyrim and Europa Universalis IV.
Thirty-seven percent of all games owned on Steam have never been played, whether because they were bought in a Steam sale on a whim or included in a bundle or just neglected somehow. For my own part, that total is probably closer to fifty or sixty percent—there are a lot of Humble Bundle games I’ve never gotten around to installing, let alone opening.

That huge backlog of games you own but never played? You’re not alone. These are just my “A”s!
And sales figure estimates are rather lower overall than I (and I expect most people) would’ve expected. A huge seller on Steam seems to top out around five or six million copies—a respectable number, but still not even close to console sales for a blockbuster title.
On the other hand, that makes it incredibly impressive that some indie games have sold over a million copies through Steam. That means they’re selling fairly well even compared to the best-selling AAA games, and probably selling a comparable amount to most AAA games on the service.
Orland’s Steam Gauge provides a fascinating glimpse into a service that’s been inscrutable up until now, and I can’t imagine Valve is too happy about it. Ars promises to release more data in the coming weeks, including a full look at how independent games are doing on the service. Until then, as I said, you can read the original full report here—it’s well worth the read and even has pretty graphs. (Seriously, you should read it.)