|1971 Phillies Arco Oil Set (via ebay)|
While the 13-card set is not as rare as I might have originally thought, it is a nice representation of the team from that era and still has a strong secondary market. At shows, you can expect to pay $25-30 for a complete set, and a scan of listings on ebay show singles have recently sold for $4-10 apiece. The cards which were sold at Arco gas stations, are 8x10", and feature white bordered color photos of the players. The front also has the player name and facsimile autograph. Backs are fairly non-descript: Player/Team names, career highlights, statistics and, of course, an Arco logo.
Card checklist (unnumbered):