[A] It is a crude oil that is found in petroleum-bearing shale formations that have relatively low porosity and permeability
[B] It is an unconventional oil produced from oil shale by pyrolysis, hydrogenation, or thermal dissolution
[C] It is an unconventional oil obtained from organic-rich fine-grained sedimentary rocks
[D] It is a colloquial term for high cost petroleum crude due to fluctuations in international crude oil prices.