As gasification reactivity of carbonaceous solid material chars is known to be strongly dependent on their formation conditions, a comprehensive study was carried out on the effects of pyrolysis conditions on structure of chars prepared from an Argentine asphaltite. The study comprised qualitative and quantitative analyses of char structures by X-ray diffraction, complemented with the characterization of physical morphology of char particles by scanning electronic microscopy and high-resolution transmission electronic microscopy. Effects of pyrolysis temperature, heating rate and holding time at the peak temperature were investigated separately in a fixed bed tubular reactor. Additionally, the overall effect of variations in time-temperature history of individual char particles was evaluated using a drop tube furnace reactor. Experimental results have shown that pyrolysis conditions have a strong influence on the asphaltite-derived char structure, producing a significant reordering of the carbonaceous matrix at high heat treatment temperatures that is evidenced by increments in aromaticity and crystalline carbon fraction. The resulting physical morphology of asphaltite-derived char particles was found to be profoundly influenced by the heating rate at which the volatile matter is released, due to the appearance of a liquid phase during the heating process. (C) 2016 Elsevier Ltd. All rights reserved.