The 2302 m deep well Weggis is situated within the northern margin of the Subalpine Molasse, in the basal part of the Rigi alluvial fan thrust sheet (Central Switzerland). The well encountered a main thrust at a drilling depth of 780 m which dips about 27° to the southeast. Eleven samples from the Lower Freshwater Molasse (USM, Oligocene) have been analyzed to study the coalification evolution. Excluding samples with reworked vitrinite, reflectance values show only a small variation, from 0.65% Rr in a sample taken at 900 m to 0.82% Rr in a sample taken at 1670 m. The relatively high near surface values (0 .71-0.75% Rr) indicate the erosion of an important sedimentary overburden (>4 km). Results from this study support a pre- and syn-thrust coalification in the Subalpine Molasse. The calculated coalification gradient of the footwall is 0.14% Rr/km and 0.08 log%Rr/km. Thermal modeling indicates that this corresponds to a paleogeothermal gradient of 20-23.5 °C/km and to paleotemperatures between 100 and 140 °C (60-70 °C higher than present-day temperatures) . The amount of calculated erosion for the well Weggis (3-4.2 km), using footwall data, can be explained by the overthrusting of a thick hangingwall sequence (Rigi thrust sheet).