The Corn 'n Oil has neither corn nor oil in it (thankfully), but it's a ridiculously tasty drink. The Corn 'n Oil gets its name from the colors of the constituent ingredients: blackstrap rum, the oil, and falernum, the corn.
If you've never heard of blackstrap rum, you're not alone. Blackstrap rum gets its name from blackstrap molasses, a bitter and intensely flavored type of molasses. Blackstrap molasses is often used as cattle feed or sold in health food stores as a dietary supplement. Sounds delicious, right?
Fortunately, a the most widely commercially available blackstrap rum, Cruzan Black Strap, takes the best part of the molasses flavor and leaves the bitterness behind. Cruzan's Black Strap is cheap and delicious, I typically see it priced in the mid-teens, and you should definitely pick up a bottle.
The original Corn 'n Oil recipe calls for just blackstrap rum and falernum, but I like to add a little lime juice. I find that the addition of lime juice brightens it up and complements the other ingredients. Serving this on crushed ice is the best way to drink it, it's a boozy drink and benefits from the dilution of the ice.