The most frequently used approach to a kinetic description of petroleum generation processes consists of determining the distribution of Arrhenius activation energies and a value for the pre-exponential factor A using open, dry pyrolysis. As a reaction system this is significantly different from the slow, confined natural processes, and it is therefore of interest to observe the applicability of the kinetic parameters to well defined test systems. Simulated maturation by hydrous pyrolysis is a well defined laboratory procedure using conditions that resemble the open pyrolysis situation more closely than the geological processes, providing a lest for the usefulness of the kinetic modelling based on the open pyrolysis parameters. In this work, seven source rocks have been matured in series of hydrous pyrolysis experiments and the open pyrolysis kinetics have been used to model the generation under these conditions. Comparison of the models to the experimental data gives good correspondence for some source rocks and large differences for others. Especially for rich source rocks, extracted bitumen yield is significantly higher than the yield curve calculated from the open system parameters. Thus, caution in quantitative use of pyrolysis based models is indicated.