Most hours spent on one game?

I have almost 5k hours on dota 2 been playing for like 5 years

I spent more than 900 hours on Garry's Mod (It's one of the best steam games, what do you expect? XD)

I have almost 10k hours on Americas army on PC. Since 2001 until 2016.

11 hours on a web game. I know really weird. But i was 10 years old and i was bored.

If you include replays in that math it's probably Front Mission 3. I tend to replay it once a year.

I think that's Garry's Mod, basically because of the rp potential of the game.

If we count games like Dota 2, then it's 3.8k hours. If not, then the second place is tied between Terraria, Civ 5 and Dark Souls: PTDE, with roughly 600 hours of play time on each of those games.

left 4 dead 2. probably around 700 hours on it/. best game ever

As of now Guild Wars 2, with 11.000 hours. I need to reconsider my life choices.

Yeah I spent about 3k hours in dota 2 over the years... kind of regret it now.