Thermal gravimetric analysis (TGA) has been used for decades to study the thermal decomposition of cellulose. Unfortunately, reported kinetic parameters extracted from TGA-based datasets for cellulose pyrolysis vary greatly; activation energies between 166 and 250 kJ/mol have been reported. In addition to heat and mass transfer limitations and source of biomass, which have previously been used to explain such variations, this work shows that the choice of regression objective function and optimization strategy are also important factors. Taking all into consideration, the activation energy of slow pyrolysis of microcrystalline cellulose was estimated to be 199 +/- 2.0 kJ/mol.