Blamish oil is a quest item used in Heroes' Quest. It is made through the Herblore skill, and it turns a normal fishing rod into an oily fishing rod. Oily fishing rods can only be used at lava fishing spots to catch lava eels.
To make Blamish oil, use Blamish snail slime and a Harralander potion(unf) (using a harralander on a vial of water). It requires level 25 Herblore to be made and gives 80 Herblore experience.
It is also a rare drop from the citizens of Canifis, that is when you defeat them entirely with the wolfbane dagger so they do not transform into a Werewolf.
Lanzig also drops this, but very rarely.
Blamish oil has a "Drink" option, but when you choose to do so, your character says, "You know... I'd really rather not."