Sour crude oil
Sour crude oil is crude oil containing a high amount of the impurity sulfur. It is common to find crude oil containing some impurities. When the total sulfur level in the oil is more than 0.5% the oil is called "sour".
The impurities need to be removed before this lower quality crude can be refined into petrol, thereby increasing the cost of processing. This results in a higher-priced gasoline than that made from sweet crude oil. Thus sour crude is usually processed into heavy crude oil such as diesel and fuel oil rather than gasoline to reduce processing cost.
The majority of the sulfur in crude oil occurs bonded to carbon atoms, with a small amount occurring as elemental sulfur in solution and as hydrogen sulfide gas. Sour oil can be toxic and corrosive, especially when the oil contains higher levels of hydrogen sulfide. At low concentrations the oil has the smell of rotten eggs. Sour crude oil needs to be stabilized by having hydrogen sulfide gas (H2S) removed from it before being transported by oil tankers for safety reasons.
Since sour crude is more common than sweet crude in the U.S. part of the Gulf of Mexico, Platts has come out in March 2009 with a new sour crude benchmark (oil marker) called "Americas Crude Marker (ACM)". Dubai Crude (and Oman Crude) both sour crude oils have been used as a benchmark (crude oil) oil marker for Middle East crude oils for some time.
The major producers of sour crude oil include:
- North America: Alberta (Canada), United States' portion of the Gulf of Mexico, and Mexico.
- South America: Venezuela, Colombia, and Ecuador.
- Middle East: Saudi Arabia, Iraq, Kuwait, Iran, Syria, and Egypt.