Who said that "free gaming" means there is no money involved whatsoever? It could actually turn out to be very profitable. Market researcher SuperData recently released its ranking of the top 10 free-for-all online games based on the 2013 earnings.

A free online game refers to a video game allowing players to download or play it without paying. Such games use other means to generate income, such as charging money for certain in-game items like premium features and virtual goods or integrating advertisements into the game.

According to the SuperData report, Tencent achieved a dominant position last year. Its two games, "CrossFire" and "League of Legends," led the ranking, with the combined annual gross revenue of US$1,581 million. "Dungeon Fighter Online" published by Nexon ranked third, which brought in the overall revenue of US$426 million.

Let's take a look at the 10 free online games with highest revenues in 2013.

 "Counter-Strike Online"

"Counter-Strike Online" [File photo]

Publisher: Valve/Nexon

2013 revenues: US$121 million