Pyrolysis experiments with resids and isolated asphaltenes from Arabian Light and Arabian Heavy feedstocks were compared with previous experiments with Hondo and Maya feeds to determine the effect of reaction environment on reaction paths, kinetics, and mechanisms. The experiments were at temperatures of 400, 425, and 450 degreesC for holding times ranging from 20 to 180 min in microbatch reactors. Reaction products were recovered as gas, maltene, asphaltene, and coke lumps. The maltene, asphaltene, and coke product fractions were collected by a solvent extraction sequence where heptane-soluble material was defined as maltene, toluene-soluble material as asphaltene, and toluene-insoluble material as coke. Gas chromatography revealed the presence of C-1-C-5 paraffins, C-2-C-5 olefins, isoparaffins, H2S, and CO2. Results were summarized by a lumped reaction network that allowed for quantitative kinetics analysis. Comparison of relative kinetics and apparent activation energies yielded insight into thermal reaction pathways, feedstock effects, and-asphaltene environment effects. At 400 and 425 degreesC, isolated asphaltene reacted selectively to maltene. At 450 degreesC, asphaltene reacted predominately to coke. Isolated maltene pyrolysis indicated that asphaltene and coke formed in series, i.e., maltene --> asphaltene --> coke.