When were oil lamps used?

Some of the earliest known oil lamps were attributed to the upper Paleolithic era. Here stones with depressions were used to burn animal fats. It was the primary source of light. Conch and oyster shells, too, formed the earlier lamps.
The clay lamps appeared in the Bronze age (16th century BC) and were used extensively throughout the Roman Empire. These lamps resembled the saucers with floating wicks.