It's about 30%. That's all you need to remain invisible to mosquitoes...and since people don't sweat, you never need to worry that it will become diluted. ;D
You can still get 80% DEET Muskol in the US, which is what I tend to use. They also sell a 45% version.
Used to be something called REPEX in Canada, but it's been many years since I saw it.