I read when I was searching info a while ago that PG has a longer shelf life than VG. Not exact what im recalling but along the lines of PG lasting a couple of yrs longer than VG. I tried to find where I saw that but couldnt. How much they both are good for I cant recall. It wasn't huge time frame, just something like VG 2 and PG 4, just to give an idea. Who knows, may be wrong but I'd guess they wont last indefinitely.