The Oil-Sucking Eels were giant sea monsters apparently native to the oceans just offshore of Megakat City. Roughly the size of a small ocean liner, these eels are eyeless, and have enormous suction-cup mouths rimmed in sharp fangs, similar to a lamprey. They have rows of spines on their backs that they are capable of flinging off their bodies at targets, as when one impaled the wing of the Turbokat. Feeding on oil, the giant eels were known for attacking oil tankers out at sea.
Two oil-sucking eels were faced by the Swat Kats, one before their involluntary trip into the Dark Ages, and one after. The first was attacking a KatCo tanker, threatening to sink it with its massive weight, but was pried off with a Pincer Missile. When Buzzsaw Missiles failed to pierce the eel's tough, rubbery hide, Razor tried a Match Head Missile. The eel swallowed the missile, which ignited the oil in its belly and blew it up from the inside-out (splattering its oily innards all over the Turbokat, much to the dismay of T-Bone).
The second eel was encountered by the Swat Kats after they'd returned from the Dark Ages after getting sucked through a Time Vortex. Like its predecessor, this eel was menacing a helpless KatCo tanker. Although they were out of missiles, having used them up in the battle with the previous eel as well as Pastmaster's dragon in the Dark Ages, they did have a ready supply of the incredibly spicy pepper stew. Although the outcome of their battle with the second eel was never seen (as the episode ended at that point), one can readily surmise that the Swat Kats made good on their promise to give the miscreant monster "a taste of Dark Age indigestion he'll never forget!"