Best-selling Steam games of 2015 list has a few surprises

Steam's massive. So massive that it recently surpassed the 12m concurrent users mark. That's an incredible 4m up from the same period a year ago.

But a new list published by the brain behind Steam Spy breaks down how massive Steam is with the best-selling games released in 2015 - and the amount of money they made.

Now, it's important to note that Steam Spy isn't 100 per cent accurate. It presents data provided by Valve that reveals the number of "owners" of a game. Steam Spy creator Sergey Galyonkin says "owned" does not mean "sold". The figures include games bought on Steam, in retail and then activated on Steam, bought in bundles through promotions as well as copies temporarily given away on free weekends. It's also worth noting games without Steamworks support sold on Origin, Uplay and GOG are not included. So, there's a margin of error here. But it's generally agreed that Steam Spy is accurate enough to be useful.

So, onto the list. It was published by Galyonkin as part of an article on Medium that estimates over 3000 new games were released on Steam in 2015 - that's up from 1900 in 2014. The paid Steam games market was worth over $3.5bn in 2015. That's an eye-watering figure, but as Galyonkin notes, it does not include free-to-play titles or downloadable content. So in some cases developers are making even more money from their games.

The list stars Rockstar's Grand Theft Auto 5 in top spot for both sales (3.8m) and revenue ($161m) in 2015, as you'd expect. Bethesda's post-apocalyptic role-playing game Fallout 4 is in at second, with an estimated 2.7m sales and $122m in revenue.

From there, though, things get interesting. ARK: Survival Evolved was a monster hit, with an estimated 2.3m sales making $14m for publisher Studio Wildcard. Rocket League made $30m. Survival game H1Z1 made $33m from 2.1m sales, and is fifth in the Steam best-sellers list. Then we have Paradox's Cities: Skylines, followed by Besiege, both of which outsold The Witcher 3 on Steam. Dying Light and Life is Strange make up the rest of the top 10.

Further down the list we see the likes of Undertale, Killing Floor 2, Elite: Dangerous, Pillars of Eternity, The Escapists and Darkest Dungeon all make impressive amounts of money. Obsidian took to Kickstarter to raise just shy of $4m for old-school fantasy role-playing game Pillars of Eternity. Given the game generated $21.5m in revenue on Steam, it's safe to say the project worked out for the developer.

The list is for games released in 2015. If we look at all games on Steam by revenue made from April to December (left in the image above), we see Valve's eSports-fuelled first-person shooter Counter-Strike: Global Offensive continues to sell in huge numbers, with an estimated 4.6m copies shifted. Not bad for a game released in 2012. Bohemia's military sim Arma 3 is still doing the business, too, with 579,000 sales. That's worth around $16m in revenue. And it's interesting to see Firaxis' strategy game Civilization 5 continue to pull in the punters. In 2015 it sold 950,000 copies, according to Steam Spy, making $11.5m. Civ 5 came out in 2010. That's a tidy earner.

So, there's a tonne of money to be made by developers and publishers on Steam. And the platform's continued growth is good news for Valve, which takes a 30 per cent cut of game sales. No wonder Gabe Newell has enough cash to invest in bizarre cooking startups.

Still no Half-Life 3, though.