Oxidation catalytic converters (oxi-cats) reduce the amount of carbon monoxide, hydrocarbons and formaldehyde in the combustion exhaust gases. They use oxidation to convert gaseous pollutants into harmless substances (carbon dioxide (CO₂) and water (H₂O)). The resistance to sulphur is geared to the relevant operating conditions. In stoichiometric operation (lambda=1), a three-way catalytic converter can reduce carbon monoxide (CO), hydrocarbons and nitrogen oxides (NOₓ) in the exhaust gas.