Debate surrounds biomass co-pyrolysis: can thermal decomposition be modeled as the sum of individual components, or do synergistic reactions promote or hinder devolatilization? Activation energies of mixtures of starch and cellulose pyrolyzed at 10, 50 and 100 K/min were determined via the distributed activation energy model. Reaction kinetics suggest that blending may promote devolatilization, seen through lower activation energies. Yet, evolved gas analysis shows no evidence of synergism as a result of blending, at least at lower temperatures. As the percentage of cellulose increases, the temperature at which the peak mass loss rate occurs and peak evolved gases emerge are linearly related. As such, there is little evidence of chemical reaction synergism during the pyrolysis of these two biomass building blocks, but rather synergistic behavior is perhaps a result of the starch physically promoting the devolatilization of cellulose at lower temperatures when present in larger quantities. (C) 2015 Elsevier B.V. All rights reserved.