This paper proposes an XML encoding standard for product catalogs, the BMEcat format. So far electronic shop systems and procurement systems use different formats for catalog data. Consequently, suppliers have to support multiple data formats. A standardization with BMEcat simplifies the exchange of product data catalogs between suppliers and buying groups on the one hand and a unique classification of articles depending on their features on the other hand. Furthermore, different types of transactions (using different parts of a product catalog) can be defined such as the transfer of a whole catalog or a price update for instance.