The Mobil guide by Henderson and Benjamin is helpful with this stuff, but I've learned mostly by the same methods as others on here, going to shows, watching lots of auctions, specializing in Mobil, etc. I was told when I first starting collecting old gas items that I better pick a brand because the amount of collectibles was overwhelming. I loved the Pegasus since I was a kid, so decided on Mobil as my main brand to collect, but like many others if I see something I like or at a good price from another brand, I'll buy it lol. So now I have Texaco, Pure, Gulf signs, cans, etc. It's easy to do in this hobby.