An exhaust gas emissions reactor and method of treating exhaust gas. The reactor has a housing for receiving exhaust gas from an engine. An oxidation catalyst is disposed in the housing for receiving exhaust gas from an inlet, and at least one mixing duct in the housing receives exhaust gas from the oxidation catalyst. An injector introduces reduction agent into the exhaust gas in the mixing duct, and at least one mixer effects mixing of exhaust gas and reduction agent. Disposed in the mixing duct downstream of the injector is an SCR catalyst for receiving exhaust gas/reduction agent mixture therethrough. Treated exhaust gas is conveyed to an outlet of the housing.