I remember these promotions as a kid, since my father always bought Fords and always filled them with Shell gasoline. The medals were received with any purchase meeting a certain minimum, and they were enclosed in flexible, white plastic envelopes that looked very much like condom wrappers. Each series had one entry that was nearly impossible to find, and only by having them all would players win the grand prize. The best remembered series was the one for U. S. presidents, which ran around 1968. The key to that game was Warren G. Harding, and I never saw that one in aluminum. Lesser winners would receive a complete set of the medals coined in brass and mounted within a decorative cardboard holder. A fellow collector's father ponied up to simply buy the complete set in brass, and I was quite envious at the time.