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.

Oil containing free sulfur or other sulfur compounds whose total sulfur content is in excess of 1 percent.

Crude oil with a high sulphur content.

Crude oil that has a high sulphur content. On the other hand, crude oil which has a low sulphur content is said to be "sweet".

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".