Near-normal-incidence reflections have been used to image the Moho and the W reflector structure in the lithosphere, offshore northern Scotland. To determine the impedance variations at these reflectors, we use a Monte Carlo technique which allows incorporation of geologically realistic a priori information as well as an extensive exploration of the model space, after testing it on a synthetic data set. The method is based on Bayesian inversion theory. The modeled Moho consists of a series of layers with a total thickness of ~2.4¿0.3 km with an overall positive impedance contrast. Inversion of the W reflector results in a model of five-seven layers with a total thickness of about 3.7¿0.6 km and mostly nonpositive impedance contrasts. The implied fine-scale impedance structure of the Moho is consistent with the broader velocity structure determined from previous wide-angle reflection/refraction profiles. However, the overall nonpositive impedance contrast at the W reflector requires a structure which is overlain or underlain by a broad increase in velocity in order to match amplitudes of reflected phases observed at large offsets interpreted previously to originate at a similar depth.¿ 1997 American Geophysical Union