Or HaChaim on Numbers 15:4/אור החיים על במדבר ט״ו:ד׳

1 והקריב המקריב קרבנו, When the person offering his sacrifice is about to do so, etc. An examination of the relative amounts of oil which are to be part of the meal-offerings appears at first glance to be proportional to the amounts of solids used in those offerings, i.e. the amount of flour. Similarly, the amount of wine which accompanies an animal sacrifice as a drink-offering is also proportional to the size of the animal being offered as a sacrifice. Why does the Torah make an exception to these proportions (compare verse 6) in our verse when the amount of flour used in the meal-offering is one tenth of an eyphah, i.e. a quarter hin which is equivalent to three lugin? [this is a proportionally much larger amount of oil than with other sacrifices. Ed.] Please refer to the Mishnah in Menachot 107. Maimonides writes in chapter 17 of his treatise on Maaseh Hakorbanot that "someone may voluntarily donate, or promise by means of a vow, a drink-offering to consist only out of wine, provided the minimum quantity is two lugin. He is not allowed to donate an offering consisting entirely out of oil even if the quantity is 2 lugin oil, as we do not find meal-offerings containing such a small amount of oil. One may also not donate one log or two lugin wine, however, as the drink-offerings accompanying animal offerings require larger amounts of wine than that." Thus far Maimonides on the subject. This may be the reason why in our verse the Torah is not satisfied with the person offering the meal-offering donating two lugin oil to be mixed with the tenth of the eyphah of flour although when the amount of flour in the meal-offering consists of two tenths eyphah of flour, the Torah had stated that 4 lugin oil are required. This is to teach you that a drink-offering of wine must not consist of less than two lugin of wine.

2One may be tempted to argue that this reasoning is only correct concerning the amount of wine in the respective drink-offerings, seeing that according to Rabbi Tarfon (Zevachim 91) an offering consisting of oil only is acceptable even in a relatively small amount. We find a difference of opinion in the Talmud Menachot we have quoted, one sage holding that one may donate as little as one log of oil as a separate offering. According to the reasoning presented in the Talmud for this latter opinion, why did the Torah not remain consistent in its presentation of the relative amounts of oil and flour? We may have to conclude that the Torah was anxious to equalise the respective amounts of oil and wine to be used in these drink or meal-offerings respectively which accompany the animal offerings.