 Due to insufficient quantity of natural gas condensate in Alberta, bitumen shippers also use refined naptha and synthetic crude oil (SCO) as diluent, and import a considerable amount from the U.S.Although SCO requires a higher volume percentage to achieve the same viscosity, at least one study found that SCO provides better blend stability than NGC.Shippers dilute bitumen before shipment in order to meet viscosity and density requirements found in common carrier pipeline tariff rules.