I will guess this movie was from between 1960-70, not sure, I was a small kid but it gave me nightmares.
The monster is like THE BLOB, but an oil slick/slime that went about and ate/dissolved people. All that would be left behind was their clothing. I think a part of movie took place on a boat, oil rig or something out in ocean. I wanna say that maybe it was even from 1950's because I think the men were wearing business suits and hats. I also think it was black and white, not sure.
And no, not a star-trek Episode. Not The Raft Thanks