An exhaust system for a diesel engine comprising an oxidation catalyst for treating an exhaust gas from the diesel engine and an emissions control device, wherein the oxidation catalyst comprises: a first washcoat region comprising platinum (Pt), manganese (Mn), a first support material and a hydrocarbon adsorbent, which is a zeolite, and wherein the manganese (Mn) is disposed or supported on the first support material; a second washcoat region comprising a platinum group metal, manganese (Mn) and a second support material comprising a refractory metal oxide, which is alumina doped with silica in a total amount of 0.5 to 15 % by weight, wherein the platinum group metal is selected from the group consisting of platinum and a combination of platinum and palladium, and wherein the platinum group metal is disposed or supported on the second support material, the manganese (Mn) is disposed or supported on the second support material; and a substrate having an inlet end and an outlet end, wherein the substrate is a flow-through substrate; wherein the first washcoat region and the second washcoat region have different compositions, and the first washcoat region is a first washcoat zone disposed at an inlet end of the substrate and the second washcoat region is a second washcoat zone disposed at an outlet end of the substrate, such that the second washcoat region is arranged to contact the exhaust gas at the outlet end of the substrate and after contact of the exhaust gas with the first washcoat region; and wherein the emissions control device is a selective catalytic reduction catalyst, a selective catalytic reduction filter catalyst, a diesel particulate filter, or a catalysed soot filter. a first washcoat region comprising platinum (Pt), manganese (Mn), a first support material and a hydrocarbon adsorbent, which is a zeolite, and wherein the manganese (Mn) is disposed or supported on the first support material; a second washcoat region comprising a platinum group metal, manganese (Mn) and a second support material comprising a refractory metal oxide, which is alumina doped with silica in a total amount of 0.5 to 15 % by weight, wherein the platinum group metal is selected from the group consisting of platinum and a combination of platinum and palladium, and wherein the platinum group metal is disposed or supported on the second support material, the manganese (Mn) is disposed or supported on the second support material; and a substrate having an inlet end and an outlet end, wherein the substrate is a flow-through substrate; wherein the first washcoat region and the second washcoat region have different compositions, and the first washcoat region is a first washcoat zone disposed at an inlet end of the substrate and the second washcoat region is a second washcoat zone disposed at an outlet end of the substrate, such that the second washcoat region is arranged to contact the exhaust gas at the outlet end of the substrate and after contact of the exhaust gas with the first washcoat region; and wherein the emissions control device is a selective catalytic reduction catalyst, a selective catalytic reduction filter catalyst, a diesel particulate filter, or a catalysed soot filter.