A dark viscous substance is a thick, sticky liquid that is often black or dark brown in color. TAR, GEL, GOO, OIL, GOOP, goos, GUNK, and BITUMEN are all examples of dark viscous substances. TAR is a type of asphalt that is used for paving roads and sealing roofs. GEL is a jelly-like substance that is often used in cosmetics and food products. GOO is a thick, slimy liquid that is often used as a lubricant. OIL is a liquid hydrocarbon that is used for fuel and lubrication. GOOP, goos, and GUNK are slang terms for any type of sticky, slimy substance. BITUMEN is a type of petroleum product that is used to make asphalt.