Most hours spent on one game?

csgo definitely, I have over 6k hours steam played.

Garr's Mod, I have 3314 hours on it. But on ARK Survival Evolved I have 3215 hours on it.

I actually have over 4k hours on original Binding of Isaac on steam, god knows why, I just loved it.

CSGO 1300+
Minecraft - 10000+
Forntite 1000+

Minecraft best game ever C

most hours i got in steam on Counter-Strike: Global offensive 903hours.

i've spent thousands of overs on smash bros. for the 3ds and smash bros. melee. countless hours on the entire series as a whole. i've spent a couple thousand on minecraft as well

Ive spent thousands of hours on online game and mobile games

I have around 4,000 hours on garrys mod lol. rip :(

I would say the longest game I spent time on was COD:Bo2, I master prestiged like 15 times. Game was fun, what can I say xd

probably the 800+ hours i've logged between the various versions of Skyrim.