Analytical studies have been performed on effluents issued from thermal conversion of Safaniya Vacuum residue (Arab Heavy) in presence of tetralin, thiophenol and methyldisulfide. In contrast to thermal behavior of the heavy oil alone, low coke amount was produced at high conversion level (up to 50%) beside good product qualities as demonstrated from analysis of the remained 500°C+fractions. H-donor diluent and sulfide additives help effectively in lowering the carbon residue values and maintaining the H/C ratios at the highest values compatible with the conversion. Microstructural parameters of the liquid effluents and their asphaltenic parts are obtained1H and13C NMR spectroscopy and average molecular weight determination. Even at high conversion level results allow to assess a rapid dealkylation process at the first stage of the thermal treatments associated with a good control in the evolution of the size of polyaromatic units. Optical Microscopy and X-ray analysis outline the specific effect of tetralin as a. delayed coking additive.