Crude oil is the world's most actively traded commodity.  Light, sweet crudes are preferred by refiners because of their low sulfur content and relatively high yields of high-value products such as gasoline, diesel fuel, heating oil, and jet fuel.  Contract size is 1,000 barrels.  Quoted as US dollars per barrel.  Settlement type is physical.  Refer to the following link for full specifications:

http://www.cmegroup.com/trading/energy/crude-oil/light-sweet-crude_contract_specifications.html