Pure fantasy: blazing walls of lit oil, bombs fashioned from bottles of oil with a lit wick, tossing oil on an enemy and setting them on fire.
None of this is even close to realistic. Lamp oil is made from vegetable oil or maybe fish oil. These oils have a flash point in the range of a two to three hundred degrees. What does this mean to the non-engineer? OIL DOESN'T BURN.
Flash point is a property of liquids; it is the temperature at which the vapors from a liquid will burn when in contact with an ignition source. When oil is underneath this temperature, it cannot be ignited. So all of these oil bombs and puddles of oil suddenly turning into a raging conflagration are all wrong.
Quick science experiment for people who do not believe me: Grab some vegetable oil from your pantry and pour it into a dish. Light a match and hold it above the oil. Does the oil burn?
No, seriously, go and do this then come back if you don't believe me. I'll wait.
Oil does burn, that is why lamps were fueled by oil. However, the oil has to be heated first before it will ignite. How do we accomplish this? With a lit wick. The wick heats the nearby oil above the flash point causing the oil to give off enough vapors to sustain a flame. That's why you start an oil lamp (or candle, same principle) by lighting the wick for a few seconds with an external fire source before the flame will catch.
[On the other hand, modern petroleum products ignite easily. The flash point of gasoline is around -44 degrees. Kids: don't play with gasoline.]
If you just had a bottle of oil and poured it on the ground, you are never going to get it to ignite with a torch. If you stick a wick into a bottle of oil and light it, the wick will burn. But if you throw that bottle and it shatters, the oil will not ignite and the flame will be snuffed out. Remember, only a tiny portion of the oil very close to the wick is hot enough to burn.
Ok, so that is a mild pet peeve off my chest. If you are bothered by basic physics, don't let your players and monsters toss around molotov cocktails made from vegetable oil. I don't.