Transportation of crude oils has recently received more attention than in the past; the main reason for this is because of the changes that petroleum production has experienced. The increasing availability of heavy and extra-heavy crude oil and the depletion of the production of light crude oil have motivated the midstream oil sector to search for methods to reduce the viscosity to values that ensure the transportation of crude oils by pipeline. The target for viscosity varies according to the type of crude oil and the region where it is transported. In order to define and propose a range of viscosity, the different reports in the literature were reviewed and it was concluded that the maximum value of-viscosity to allow crude oil transportation ranges between 250 and 400 cSt at 37.8 degrees C.