Pope Shenouda III
The lamps, which are lighted by oil, have a spiritual meaning. The oil is a symbol of the Holy Spirit, It was used for anointing, after which the Spirit of the Lord descended: When Samuel anointed David, the Spirit of the Lord came upon him in power (1Sam.16: 13). The Holy Bible also tells us about the anointing from the Holy One (1John.2: 20,27).
Even the candles which we light in church are made of oil, and the lamps in church are lighted by oil for the same symbolic significance.