Exhaust system for a spark-ignited internal combustion engine

An exhaust system for a spark-ignited internal combustion engine comprising:

• (a) a three-way catalyst (TWC) composition including an oxygen storage component, wherein the TWC composition is coated on a flow-through monolith substrate, the substrate comprises a plurality of channels, and each channel has a length extending from an inlet end to an outlet end;
• and
• (b) a single lambda sensor,
• wherein the substrate comprises a portion of the plurality of channels, wherein the portion of the plurality of channels is annular in shape, wherein the TWC composition in at least a part of the length of channels extending from the inlet end has a reduced oxygen storage activity, or no oxygen storage activity, relative to the TWC composition in a remainder of the substrate, the arrangement being such that the single lambda sensor is contacted substantially only with exhaust gas that has first contacted the TWC composition having a reduced oxygen storage activity or no oxygen storage activity.