Abstract: Apparatus is provided for mixing an oxygen containing gas, for example air, with exhaust gas from a liquefied petroleum gas (LPG) fuelled internal combustion engine, the mixture bieng supplied to a catalytic converter to reduce the level of carbon monoxide in the exhaust gas. The apparatus comprises a first duct for supplying the exhaust gas to a catalytic converter, and a second duct having a closed end extending transversely into the first duct for supplying air to mix with the exhaust gas. Opening means are provided in the wall of the second duct to allow air, pumped under pressure to the second duct by an engine driven pump, to flow into and mix with the exhaust gas.