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 of their craft. These are tailored to damage specific types of foes.
To have access to any type of oil, player must first craft said oil which require specific diagrams that are spread across the world, either as loot or merchant's item.
Crafting oils in Wild Hunt is done through the alchemy menu while out of combat, but they can be applied to weapons at any time. Similar to potions and bombs, once an oil is crafted, it remains in your inventory, oils do not need to be replenished however.
Oils can be applied to swords from the Inventory window, with Hanged Man's Venom reserved for Steel weapon and most other oils being exclusive to Silver swords. Beast oils 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.
Oil functionality can be expanded by investing Ability Points in the Oil Preparation segment of Alchemy Branch in Character skill tree.
There are as many oils as classification of enemies which they're exclusively effective against, each can be upgraded into two higher tiers which are Enhanced and finally Superior versions which provide higher multiplier and bigger charge than the previous tier
Oils do not last indefinitely and it's 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. 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 skill node, however, 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. The Grandmaster Wolven Gear 3-pieces set bonus allows 2 different oil effects on a single sword.