Zevachim 91 - Digression: Laws of Flour and Oil Offerings
Said Rabbi Shimon, "If you see Kohanim who are distributing oil in the Temple Courtyard, you don't have to ask what it is. It is either the remainder of a wafer flour-offering of a regular Jew, or the remainder of the oil of a metzora, a spiritual leper. (Only Rabbi Shimon thinks so, but the Sages say that the oil was smeared on the wafer until none remained.)
Rabbi Shimon continued, "If you see oil being poured upon the fires of the Altar, again you don't have to ask what it is; it is either the remainder of a wafer flour-offering of the Kohanim (for their flour offerings was completely burned), or it is the remainder of the daily flour offering of the Anointed Kohen. Rabbi Shimon's opinion is that one is not allowed to donate oil as an offering. However, Rabbi Tarfon says that one may donate oil.
Art: Rembrandt Van Rijn - Dr Ephraim Bueno, Jewish Physician and Writer