Multiple choice Petroleum is known as black gold, because _________. it is black coloured. it is dark brown and viscous crude oil. its demand is very high. it is dark brown crude oil which has great commercial importance. Reveal answer Fill a bubble to check yourself D Correct answer Explanation Gold refers to a substance, which is either very costly or has got a high commercial value. Petroleum is called black gold because of its dark brown colour and its great commercial importance.