Basilisk Oil

Basilisk Oil is a magical compound which appears in  Ultima Underworld II.

Description
To the unlearned eye, basilisk oil appears to be a clear-colored potion, similar to the variety commonly used to restore spellcasters' mana. In reality, it is a potent hallucinogenic which may be used in ritual magic, in particularly the binding of air djinn. During the course of their quest to shatter the Blackrock Dome which had enveloped Castle Britannia, the Avatar would have need of basilisk oil, which they mixed with the filanium mud of Anodunos in preparation for sealing a such a djinn into their own body.

Locations
Basilisk oil may be found at the following locations in the course of Ultima Underworld II:
 * Castle Britannia, Level 2 (one container may be found in a cache guarded by two gazers)
 * Scintillus Academy, Secure Vault (in a chest in the outer vault)
 * Pits of Carnage, Level 1 (one container may be found in Zaria's quarters)
 * Pits of Carnage, Level 3 (three containers may be found in the secret quarters of a liche)

Trivia

 * It is very easy to waste all the Basilisk Oil and thus create an unwinnable situation, as one can't identify it until the Lore skill is high enough and also its importance may be unknown. The very difficult to reach locations of the later potions seem to be chosen by the programmers to ensure the player would know about the oil when finally finding them.