Abstract
Currently, more than half of the oil reserves (53.3%) in the world are in the form of restorable oils such as heavy oil, extra heavy oil, oil sand, tar sands, oil shale, and bitumen. Heavy oil is one of the petroleum oil varieties that contain long chain hydrocarbons. All types of heavy oils contain asphaltenes and thus are considered very dense substances. The asphaltenes are one of the most complex and heavy organic compounds present in the heavy oil. The heavy oil is defined as one having an American Petroleum Institute scale index equal or smaller than 20 degrees. In conventional refining procedures, heavy oil poses many challenges. Recycling and re-refining are applied techniques for the processing of petroleum based heavy oils into reusable light oils such as gasoline and diesel fuel. In this regard, catalytic pyrolysis and thermal cracking are promising technologies for light oil production. The authors review the heavy oil upgrading processes and their associated challenges with ambition to find cost-effective ways to ensure a constant future fuel supply.