The aim of the MMU-project was to investigate whether a petroleum play is present around the MMU. One of the hypotheses that was tested, encompasses the presence of a basin floor fan of Serravalian age. Interpretation of the gas composition data revealed the existence of two petroleum systems around the Miocene unconformities. Gas of predominant thermogenic origin occurs in Cenozoic sequences below the MMU/LMU (and slightly above it) overlying the F17 and Hanze Chalk fields. There is no apparent change in thermogenic gas composition in the Lower North Sea Group sequences. Abrupt changes in gas composition from predominant thermogenic to predominant microbial signature occur above the MMU/LMU. Gas composition in the Eridanos Delta deposits above the MMU/LMU has a strong microbial signature. Leakage of thermogenic gas from the F17 and Hanze Chalk fields into the Cenozoic caprocks occurred in Gelasian times and/or later. Microbial generation of gas in the Eridanos Delta deposits started at the beginning of the Gelasian and continuous until present day.