Harvesting Whale Oil is a book found in The Knife of Dunwall.
[Excerpt from a manual on draining whales and refining the oil]
In earlier years, the methods used to reclaim whale oil from blubber were both inefficient and dangerous. The original technique required the raw blubber to be sealed in pressurized cookers which forced the volatile fluid out of the tissues and into collection tanks. The refined oil was then cooled rapidly while the pressure was reduced, and if the synchronization of these processes was not perfect, it was possible for the oil to release all of its energy in a devastating explosion. This is believed to be the cause of the historic Fullerton Whalehouse explosion that cost over 150 lives.
Modern industrial trends have reduced the dangers of collection while increasing the output from each creature. Greaves Refinery made the first steps in live collection, aided by research from the Academy of Natural Philosophy. In the wake of the plague, Greaves has suspended operations, and this process is now applied at the Rothwild Slaughterhouse. No longer is the whale blubber removed and harvested, but instead the very mechanism that creates the oil inside the whale is stimulated, and the resulting oil is drained away and stored. This results in a more stable raw oil that is easier to refine, with more tanks harvested from a single whale.
It can be found in the Rothwild Slaughterhouse on the Killing Floor in the room with the live whale during the mission A Captain of Industry.