Triaxial compression tests were carried out on Toarcian source rocks (Lias ε) from South Germany under various temperatures between 20 °C and 300 °C and under drained and undrained conditions. The behavior of the source rocks with high total organic carbon (TOC) is strongly temperature dependent and predominantly plastic at elevated temperatures. Microfracture systems are generated which resemble natural assemblages. The fractures are of tensile nature and related to internal pressure built-up in the pore fluid. The experiments provide new aspects to compaction and fluid expulsion from source rocks.