Membranes fulfill many different functions inside a cell and have consequently been in the focus of biophysical studies for several decades. High resolution structure analysis of model membrane systems by x-ray reflectivity is typically performed using stabilizing solid supports, which have shown to strongly interact with the membranes and can severly affect the membrane`s functionality. To circumvent these restrictions free-standing lipid model membranes, also called Black Lipid Membranes (BLMs), have been used in this work towards a novel type of structural assay based on x-ray phase contrast imaging. Bulged lipid bilayers fully immersed in buffer solution have been visualized by a transmitted plane or spherical x-ray wave front in the Fresnel regime after free space propagation. The development of the experimental system and the image analysis enables a quantitative investigation of the membrane`s structural properties in a localized membrane patch. In future this technique can be used to study the structure of membranes and more generally ultrathin films in functional and physiological environments and under out-of-equilibrium conditions.