Chemical properties

Heavy oil is asphaltic. It is "heavy" (dense and viscous) due to the high presence of naphthenes and paraffins. Heavy oil has over 60 carbon atoms and hence a high boiling point and molecular weight. For example, the viscosity of Venezuela's Orinoco extra-heavy crude oil lies in the range 1000-5000 cP, while Canadian extra-heavy crude has a viscosity in the range 5000-10,000 cP, about the same as molasses, and higher (up to 100,000 cP for the most viscous commercially exploitable deposits).A definition from the Chevron Phillips Chemical Company LP website is as follows:
The "heaviness" of heavy oil is primarily the result of a relatively high proportion of a mixed bag of complex, high molecular weight, non-paraffinic compounds and a low proportion of volatile, low molecular weight compounds. Heavy oils typically contain very little paraffin and may or may not contain high levels of asphaltenes.