Pliny the Elder (23-79 C.E.) was the first to record the practice, which he learned from Roman sailors.
Saint Bede the Venerable, around the year 731, may have been the first to set down the phrase: "Pour oil on troubled water." Bede related the story of Saint Aidan (d. 651), giving a cruse of oil to a young seafaring priest to calm the waves if they got rough.
It actually works. Here is a link to a video in which you can watch a rippled puddle turn glassy smooth. It's also been observed during ocean storms. Commodore Wilkes of the United States Navy saw it happen off the Cape of Good Hope when oil leaked from a whaling ship.
Who first used the phrase as a metaphor? Was it founding father Benjamin Rush? "His presence and advice, like oil upon troubled waters, have composed the contending waves of faction."
Or was it the better known Benjamin, Ambassador Franklin, who both ran experiments on the phenomenon and referred to the effect in letters about matters of state?
It's a nice metaphor, but hopelessly obsolete given the present environmental catastrophe. Oil on the Gulf waters has composed exactly nobody, and to use the phrase now will ever be an invitation to being misunderstood.
The Venerable Bede, woodcut from the Nuremburg Chronicle, 1493--one of the earliest printed books. The artist was either Michael Wohlgemut (1434-1519) or his stepson Wilhelm Pleydenwurff (c. 1450-1494). Possibly Wohlgemut's young apprentice lent a hand: Albrecht Dürer (1471-1528). Click on the picture for a closer look.