Petroleum

Petroleum, also known as oil, tar, naphtha, rock oil, or earth's blood, was a noxious and dangerous liquid mineral substance found in the Realms. Vaguely similar to common pitch and oils derived from plants and animals, it instead came from beneath the earth.

Description
Oil was a thick black liquid that gave off stinking, deadly fumes, and ignited and exploded very easily when exposed to flames and sparks. It produced a watery-looking flame and thick, greasy, stinking smoke when burned.

Availability
Rock oil existed in deep underground deposits scattered across Faerûn, and included naturally formed bitumen. On occasion, these deposits welled up and made themselves known on the surface, forming tar pits or floating atop water, poisoning the ground and water around it. More commonly, the empty spaces of the Underdark interrupted the upward flow of the liquid, and so most revealed oil deposits were found in these deep caverns.

Extremely large deposits of pooled rock oil could be found in the Underdark beneath the Eastern Shaar, as well as south and east towards the Raurin desert and the Shining Lands.

Surface tar pits could be found across the Realms, and these surface deposits had a tendency to trap and drown animals like goats and sheep. They were especially common in the Shining Lands of Veldorn, Var, Ulgarth, and nearby Utter East, as well as in Chult, the Alimir Mountains, and isles of the Lake of Steam. Tar pits could also form due to great magical forces, such as in the Helmlands and in Myrloch Vale.

Usages
Rock oil was mainly known for being a natural hazard thanks to its poisonous and flammable nature. The oil could be used as a fuel, but was rare compared to commonly-available fuels such as charcoal and animal or plant-based oils. It could also be distilled and refined into other useful substances such as bitumen.

A refined form of oil known as naphtha was a useful flammable agent. Alchemists used naphtha to make sticky, burning concoctions such as alchemist's fire, everburning oil, oil of fiery burning,   loaded into a flame thrower, or delivered alongside another flammable weapon. Naphtha could be used as part of traps that sprayed intruders with the substance, ideally followed up by them being set aflame.

The image trap spell used a figurine of the caster soaked in naphtha.