1. n. [Heavy Oil, Enhanced Oil Recovery]
Crude oil with high viscosity (typically above 10 cP), and high specific gravity. The API classifies heavy oil as crudes with a gravity below 22.3° API. In addition to high viscosity and high specific gravity, heavy oils typically have low hydrogen-to-carbon ratios; high asphaltene, sulfur, nitrogen, and heavy-metal content; and higher acid numbers.
Synonyms: viscous oil
See: crude oil