The Beis Yosef asks a very famous question regarding Chanukah: Why are there eight nights of Chanukah when the miracle seemingly only lasted seven nights? The oil that was found was sufficient to last for one night, yet it miraculously lasted for eight nights – in other words, seven nights longer than it was supposed to.
(As a side note, there are two reasons given for why the Jews at the time needed to wait eight days for new oil to be made. One is that everyone in Klal Yisrael was tammei, and no one could produce oil that would be tahor. Therefore, they needed to undergo the seven days of the para aduma purification process and then spend an additional day making oil. The Ran suggests that tahor oil was available, but it was a four-day journey’s distance away. Thus it took four days to get it and four days to return with it to the beis hamikdash.)
The Beis Yosef’s question is actually found in an earlier source – the Me’iri (Shabbos 21b) asks this question as well – and hundreds of answers have been offered over the years. The Me’iri suggests that we observe one day of Chanukah to celebrate the military victory. The other seven are to commemorate the miracle of the oil.
The Beis Yosef suggests three answers. One of his answers is that when the kohanim realized that they needed eight days to make new oil, they divided the jug of oil into eight equal parts. They lit one eighth of the jug on the first night and it lasted through the night. This was repeated each night for eight nights until the new oil was ready. Thus, the miracle was repeated eight times.
The second answer of the Beis Yosef is that after the kohanim poured the oil into the menorah the jug was miraculously replenished even on the first night. The third answer of the Beis Yosef is that every morning, when the kohanim checked the menorah, they found that the oil was still in the menorah seemingly unused.
There is a glaring difference between the Beis Yosef’s answers. According to the first and last answer, the miracle was that the oil burned far longer than naturally possible. According to the middle answer, the oil was indeed used up, but new oil miraculously appeared.
Rav Chaim Soloveitchik zt”l is quoted as saying that the oil could not have miraculously replenished itself because such oil would be unfit for use. He argued that such oil would be considered miracle oil and not olive oil (shemen zayis). A proof for this contention is brought from a comment of the Radak (II Melachim 4:7) that the oil Elisha produced for the Shunamis woman was exempt from ma’aser. Elisha told the woman that she should borrow vessels from her neighbors and pour from her little jug of oil into the empty vessels. She followed his instructions, and the oil did not stop pouring from her jug until she had filled up all the empty vessels. We see from the Radadk’s comment that oil produced by means of a neis is not considered shemen zayis.
Some question this assertion from a passage in Targum Yonasan. On Shemos 35:27, Targum Yonasan states that the precious stones and menorah oil donated to the Mishkan by the Nessiyim were given to them from Shamayim. Apparently, then, oil produced by means of a miracle is fit for use in the menorah.
Rav Tzvi Pesach Frank, in Mikraei Kodesh, answers based on a comment in the Midrash Rabba (Bereishis 8:11). The Midrash states that there were actual olive trees in Gan Eden and that the yona bird Noach sent out of the teiva returned with an olive branch in its mouth from a tree in Gan Eden. Rav Frank posits that the oil given to the Nessiyim was from actual trees in Gan Eden. Therefore, there is no counter evidence to the principle put forth by Rav Chaim Soloveitchik that “miracle oil” is unfit for use for the menorah.