In this study, the investigation of pyrolysis reactions of heavy oil was aimed. Heavy oil that was provided from Raman field in the southeastern part of Turkey to use in our study, was subjected to pyrolysis at temperatures of 350, 400 and 450 degrees C for holding times ranging from 10 to 120 min using sand bath. Product fractions were separated as gas, maltene, light maltene, asphaltene and coke. The time and temperature dependence of product distributions were determined. Molecular structure of asphaltenes are characterized by elemental analysis, proton nuclear magnetic resonance (H-1 NMR), gel permeation chromatography (GPC). The effect of the heavy oil environment on the asphaltene pyrolysis was also investigated in this study. (C) 2015 Elsevier B.V. All rights reserved.