1968 Atlantic Oil contest cards. There are 40 base cards and ten prize-winners (well, 11 if you count a redemption card that could be traded for a stats booklet at the gas station). Here is the redemption card:
It is tough but not rare.
I've seen a handful of winner cards in 30+ years of chasing the set, nearly all of which were the $1 winners Osteen and Wilson. The only higher $ prize I found was this one, which is for the 2nd highest prize:
But I keep looking...