You can use 87 octane. I use it all the time. I started off using 93 octane, but I got tired of paying for the difference. I can tell the difference in performance between 93 and 87 but for the type of driving I do most times it just doesn't matter. There's been no knocking whatsoever. I've got the 2018 Terrain Denali. If I were going to keep it long term, I might would only use 93, but the reality is, there's no way I'll have this thing past 2021, probably not past 2020. I get bored quickly, haha.