Carbon isotope and molecular compositions of Cretaceous mudgases have been examined from several depth profiles across the undisturbed Western Canada Sedimentary Basin (WCSB). The complexity of the isotopic profiles shows numerous inflections and deviations of the carbon isotope values and wetness index with depth that suggest a correlation with the stratigraphic framework and can be explained in terms of the origin and alteration of the gases. However, combined evidence from a multidisciplinary approach suggests that isotopic variability of WCSB gases is only partly induced by source...