Sulfur oxides or SOx are compounds formed by the reaction of sulfur with oxgen when a sulfur-containing hydrocarbon is burned.

SOx emissions are a source of air pollution and are regulated in most markets.

SOx emission from most refined products are controlled by the maximum sulfur limit placed on the fuel.

In places where large volumes of fuel are burned (e.g., power plants), scrubbers can be used to remove SOx from the combustion gases after burning, allowing use of higher-sulfur fuel.