This paper presents a procedure to fit kinetic parameters of runaway reactions using data measured in Phi-TEC II adiabatic calorimeters. The parameter fitting is based on running multiple dynamic simulations of calorimeter experiments using a model that considers the compositional description of the fluid within the calorimeter cell and uses accurate thermodynamic models to evaluate the fluid properties, including changes to the amounts and compositions of each phase present inside the cell. In addition, the model accounts for the heat capacity of the calorimeter cell, which is considered to be temperature-dependent. This rigorous method represents a considerable departure from the simplifying assumptions embedded in the usual approach of adopting constant phi-factors for treating data measured in adiabatic calorimeters. An example of the model's application shows that the parameters fitted using the proposed method are capable of an accurate representation of the dynamics of di-tert-butyl peroxide decomposition. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.