"According to the satellite image, the slick... was about 40 kilometres (25 miles) southeast of the last known location of the aircraft. The slick is about two kilometres long," the Netherlands-based ESA said in a statement.
Search teams are scouring the Mediterranean for the remains of the Airbus A320 that suddenly disappeared from radar on Thursday on a routine flight between Paris and Cairo.
"Since the plane disappeared, ESA and experts have been scrutinising satellite data to see if anything could be found to indicate wreckage of oil floating on the sea," ESA said.
The slick was spotted at 33°32' North and 29°13' East by ESA's Sentinel-1A radar satellite, and first seen at 1800 GMT on Thursday, the space agency said.
A second image taken Friday showed that the slick drifted by about 5.0 kilometres.
"There is however no guarantee that the slick is from the missing aircraft," ESA stressed.
The news came after Greek officials said that a body part, seats and some items of luggage were found Friday off the coast of Alexandria.
The Sentinel-2A satellite will pass over the area on Sunday after which space experts will continue to study images.
Both satellites were lanched as part of Europe's environmental monitoring Copernicus programme.
The latest air tragedy raised fears that the plane may have fallen victim to a terror attack, after the bombing of a Russian passenger jet by the Islamic State militant group over Egypt in October that killed all 224 people on board.
EgyptAir had prematurely announced on Thursday that wreckage from the plane had been found floating at sea off the island of Karpathos, northeast of Crete, only to backtrack after Greece denied any debris had been found.
The plane disappeared between Karpathos and the Egyptian coast in the early hours of Thursday morning, without its crew sending a distress signal.
