Oil is added here as a fit sign of God's grace and mercy, and of the leper's healing. Log, a measure for liquid things containing six eggshells-full.
Related Commentaries of Leviticus 14:10
Leviticus 14:10
10 And on the eighth day he shall take two he lambs without blemish, and one ewe lamb of the first year without blemish, and three tenth deals of fine flour for a meat offering, mingled with oil, and one log of oil.