The structure of thin films of tungsten-carbon, deposited onto monocrystalline silicon substrates by reactive magnetron sputtering (argon + benzene) in a wide range of preparation parameters has been investigated by GISAXS. Substrates were in a fixed position relative to the two adjacent cylindrical magnetrons. Benzene partial pressure was varied from 1% to 10% of the total working gas pressure. A series of samples were prepared, with the substrate held at room temperature and 400°C, and the substrate potential held at floating potential or biased -70 V with respect to the discharge plasma. The bulk particle contribution to the scattering was investigated outside of the specular plane, applying a two dimensional CCD detector. For higher values of benzene partial pressure, the generated films consist of densely packed tungsten carbide grains in an amorphous, carbon rich matrix, while, in some cases, the lower benzene pressure resulted in isolated carbon rich particles in tungsten carbide. From earlier work it is known that the preparation parameters influence the film’s chemical composition, the relatively complex dependence of particle sizes on benzene partial pressure can be explained as a function of the relative carbon content.