This page lists the available oils in The Witcher 3: Wild Hunt.
To increase the effectiveness of their blades against foes, a witcher can coat them with special oils, tailored to each damage a specific type of enemy.
To have access to any type of oil, the player must first craft said oil, which requires alchemy formulae that are spread across the world, either at a random diagram location, purchased from a merchant, or rewarded from a quest.
Crafting oils is done through the alchemy menu while out of combat, but they can be applied to swords at any time. Similar to potions and bombs, once an oil is crafted, it will remain permanently in your inventory, though oils do not need to be replenished.
Oils can be applied to swords from the inventory window, with Hanged Man's Venom reserved for steel swords and all other oils being exclusive to silver swords, except for beast oil, which can be used on both. Oils will increase the damage of the coated swords against targeted enemy types, this enhancement is multiplocatory and is counted after abilities and other damage increasing factors, though at base value, a basic oil will add +10% attack power, an enhanced +25%, and a superior oil +50%.
Oils do not last indefinitely and their effects can expire after landing enough hits. This can be tracked with a counter that will appear beneath the Toxicity meter if Geralt has an oil-coated sword drawn. The number represents the amount of hits remaining that will have the oil's effects, it decreases with every successful strike (even against enemies not targeted with the oil), if the number reaches zero, the oil will be rubbed off, and the effect will disappear. The slowly-depleting radial green line around the counter acts as a rough indicator of how many strikes you have left. The maxed out Fixative ability allows oil effects to last indefinitely.
Traditionally, a sword can have only one active oil effect at a time. Applying a different oil will override the previous coating. In the Blood and Wine expansion, the Grandmaster Wolven Gear 3-pieces set bonus allows 2 different oil effects on a single sword.