Nope nope nope nope, oiling a blade takes time, you shouldn't be able to do it with 10 downers trying to eat your face. Also a lot of what I'm seeing in this tread is that it's hard to guess what your going to fight next and to that I say poppycock. For the most part you will always fight the same monsters in the same areas, I'm going to a swamp guess I need necrophage oil, running down the coast more necrophage oil, crossing a recent battlefield uh..... more necrophage oil.
Yeah necrophage oil is a safe bet for alot of the game.
Running around Skellige well insectoid oil for reasons. Contracts are easy because they straight up tell you what your going to be facing.
Most big monster are easily seen from far off, the flying ones are almost always flying, so if your going to engage them you have no excuse for not changing your oil. On the other big monster I personally have never been ambushed by a golem, a leshen or a earth elemental.
Steel sword are easy hang man oil or beast oil, take your pick, I normally just leave hang man oil on because there are just so many bandits around, also most beast are super easy to kill anyways.
Ideas for making oil last longer make no sense because that's already part of the game. Third level oil ability makes oils permanent with just 3 points.