Shalom aleichem. It is forbidden to keep the oil and wicks that were used to light the menorah on Chanukah, rather they must be burned. However, if someone transgressed and kept the remaining oil and wicks that didn’t get burned all the way from last Chanukah, and uses them to do the mitzvah this Chanukah, would he still be yotzei the mitzvah? Thanks a lot.
The reason we are not allowed to keep he oil and wicks from year to year is because te oil that was used for a mitzvah may not be used for other uses, and in order that we shoudn’t come to use it for other things, we burn them. However the reaon is not because they are categorically forbidden. Therefore in your case when it as already the next Chanukah, and you want to use the leftover oil for the next year’s candles it is permitted, the same way we are allowed to use the leftover oil from last night’s chanukah lights for the next night of Chanukah.
As a side point, the only oil and wicks that are for bidden to use are the actual oil and wicks that were in the menorah when it was lit. The leftover oil in the bottle, and he left over wicks that weren’t used are permitted to use for any use.
O:CH 767-4, M:B ibid 17,19, Horav Y. Cahen Shlit”a.