Abstract: The present invention relates to catalysts for reforming petroleum products in mass form or supported for example, on aluminium or active carbon, the active part of which consists of tungsten and molybdenum carbides corresponding to the general formula:(Mox W.sub.1-x)y Czwherein0<x<11.ltoreq.y.ltoreq.20.8.ltoreq.z.ltoreq.1Nitridation prior to their use in a mixture H.sub.2 +N.sub.2 substantially increases the activity and selectivity thereof.These catalysts are not very sensitive to contamination by sulphur products.