In situ stress measurements in thick limestone layers of the Parisian Basin and in neighboring regions yield a remarkably homogeneous stress field. The flat jack method has been used. Comparison with over-coring gave good agreement for the azimuth of the principal axes. In the Jurassic of Burgundy and Poitou as well as in a Carboniferous outcrop near the English Channel, maximum compression is found along the NNW-SSE direction.