An apparatus comprising a lean-burn internal combustion engine, engine management means and an exhaust system for treating exhaust gas of the engine, which exhaust system comprising: a first oxidation catalyst disposed on a first honeycomb monolith substrate, which first oxidation catalyst comprising platinum supported on a first metal oxide support, wherein the first metal oxide support comprises at least one reducible oxide, which comprises ceria (CeO 2); and wherein the first oxidation catalyst is free of alkali metals and alkaline earth metals, and the first oxidation catalyst is combined with a second oxidation catalyst different from the first oxidation catalyst; wherein the second oxidation catalyst comprises at least one precious metal supported on a second metal oxide support; and wherein the first oxidation catalyst is located in a first zone disposed on the first honeycomb monolith substrate and the second oxidation catalyst is located in a second zone on the first honeycomb monolith substrate, wherein the first honeycomb monolith substrate is oriented so that exhaust gas contacts the first zone prior to the second zone; and the first honeycomb monolith substrate has a flow-through configuration in which a plurality of channels extend in parallel from an open inlet end to an open outlet end; and the engine management means is configured to intermittently modulate, in use, the lambda composition of the exhaust gas contacting the first oxidation catalyst to a rich lambda composition; and wherein the first honeycomb monolith substrate is disposed upstream of a monolith substrate comprising a catalyst for selectively reducing oxides of nitrogen using a nitrogenous reductant. a first oxidation catalyst disposed on a first honeycomb monolith substrate, which first oxidation catalyst comprising platinum supported on a first metal oxide support, wherein the first metal oxide support comprises at least one reducible oxide, which comprises ceria (CeO 2); and wherein the first oxidation catalyst is free of alkali metals and alkaline earth metals, and the first oxidation catalyst is combined with a second oxidation catalyst different from the first oxidation catalyst; wherein the second oxidation catalyst comprises at least one precious metal supported on a second metal oxide support; and wherein the first oxidation catalyst is located in a first zone disposed on the first honeycomb monolith substrate and the second oxidation catalyst is located in a second zone on the first honeycomb monolith substrate, wherein the first honeycomb monolith substrate is oriented so that exhaust gas contacts the first zone prior to the second zone; and the first honeycomb monolith substrate has a flow-through configuration in which a plurality of channels extend in parallel from an open inlet end to an open outlet end; and the engine management means is configured to intermittently modulate, in use, the lambda composition of the exhaust gas contacting the first oxidation catalyst to a rich lambda composition; and wherein the first honeycomb monolith substrate is disposed upstream of a monolith substrate comprising a catalyst for selectively reducing oxides of nitrogen using a nitrogenous reductant.