An industry term for crude oil relatively high in sulfur content. The term sour generally denotes crude with a sulfur content of 1.5% by weight or higher. Sour crude usually commands a lower price than sweet crude of equivalent APR gravity.
Sour crude oil contains the impurities hydrogen sulfide (H2S) and carbon dioxide, or mercaptans. All crude oil contains some impurities. When the total sulfide level in the oil is > 1 % the oil is called "sour".