Sunoco I believe. I collected them as well.
Correct, it was Sunoco. I just found a bunch of them in my basement. They came in a grouping with perforations so you detach the stamps individually. Had about 40 booklets of them. Had 2 Bradshaw stamps as part of the group. It's not uncommon to still find them on EBay, either as individual stamps, books like mine, and then the most valuable which are books that are still "unopened".