Valve’s digital distribution platform Steam has announced that sales on the service increased 100 percent year-on-year in 2011.

This is the seventh consecutive year the digital retail platform has seen sales double. Valve also reports that over 14.5 million Steamworks-enabled games were registered in 2011, a 67 percent increase over 2011.

“Steam and Steamworks continues to evolve to keep up with customer and developer demands for new services and content," said Valve’s Gabe Newell. “Support for in-game item trading prompted the exchange of over 19 million items. Support for free-to-play (FTP) games, launched in June, has spurred the launch of 18 FTP titles on Steam, with more coming in 2012. Looking forward, we are preparing for the launch of the Big Picture UI mode, which will allow gamers to experience Steam on large displays and in more rooms of the house.”

Steam now boasts over 40 million subscribers and hosts over 1,800 games.