Diluents are fluids used to reduce the viscosity (thickness) of heavy oils, such as bitumen based crude oil from the tar sands, in order to thin them enough to transport through pipelines & tankcars.
Natural gas condensate is the most often used diluent in transporting crude oil in western Canada, benzene is the major componenet. Other diluents include byproducts of the refining process, naphtha,
benzene and pentane are some dilutents. When the hevy crude or bitumen is mixed and transpoted it is called Dilbit (diluted bitumen). After the crude is off-loaded the diluent is removed and reloaded into tankcars and transported back to the load-out.