NOVELTY - An exhaust system (10) has a cylindrical catalyst assembly (2) with a first catalyst (4) having a methane oxidizing catalyst and is positioned upstream of a second catalyst (6), and second catalyst having a selective catalytic reduction catalyst. An injector (16) is positioned between first and second catalysts and adapted to inject urea into exhaust system.    USE - Exhaust system for dual fuel engine (claimed).    ADVANTAGE - Enables methane to be oxidized to produce carbon dioxide and water with the first catalyst since fuelled predominately on methane when engine is running in the second mode. Eliminates need for heat sink since heat sink is dependent, inter alia, on the composition of second catalyst. Ensures efficient design of exhaust system since less space is taken up by the catalyst assembly as whole as would be the case if first and second catalysts are formed separately to one another. Ensures even distribution of exhaust gases across the face of first catalyst due to first guide with conduit that defines enclosed volume and perforate baffle that extends across the face of first catalyst. Prevents recirculation of exhaust gases emerging from the first catalyst due to wall or barrier, thus helps prevent exhaust gases re-entering the first catalyst. Ensures optimum mixing since injector has annular ring adapted to spray urea in the same direction of flow as the direction of flow of exhaust gases. Provides improved mixing and atomization process as urea is injected by injector since pressure drop through perforation reduces the flow velocity and effectively provides longer residence time of the urea within volume that helps to redistribute the urea spray and progress the thermolysis reactions to produce ammonia.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method for removing nitrogen oxide and methane from exhaust gases of a dual fuel engine.    DESCRIPTION OF DRAWING(S) - The drawing shows a detailed schematic view of a catalyst system with the flow of exhaust gases through the catalyst system.    Catalyst assembly (2)    First catalyst (4)    Second catalyst (6)    Exhaust system (10)    Injector (16)