look on Amazon... they have all the different percentages. I've never used the overnight gel, but I've heard there can be less sensitivity with the lower percentages. I just can't imagine sleeping with a bleaching tray/gel in my mouth!
I’ve used both, and feel like I saw way more results with the 10% overnight. Only thing is I started pushing out my retainer when I was asleep, so I changed to the green one (I think it’s the 35%). Stuff works very well!