Environmental problems caused by both mobile and fixed sources, such as vehicles and chemical plants, are drastically changing the main objectives of the refining industry, as cleaner sulfur-free fuels are obligatory. Therefore, the search for alternative hydrocarbon sources, which enable the traditional refiner to reduce contaminants without major investments, is very important. This paper presents the possibilities of using natural gas as a clean raw material to replace oil. The main options of catalytic chemical transformations are discussed. Gas-to-gas (GTG) transformations, yielding dimethyl ether or olefins, as well as gas-to-liquid (GTL) processes, generating medium distillates, paraffin and naphtha, or even aromatics via a different route, are discussed. Finally, the challenges in terms of the future of catalysis are also presented. © 2004 Published by Elsevier B.V.