Abstract: An inhibitor to suppress or inhibit the viscosity increase of a hydrocarbon, e.g. in a bottom section of an oil quench tower, featuring the use of a sulfonic acid and/or its salt as an effective inhibitor composition, which may optionally contain a polymerization inhibitor including one or more inhibitors selected from the group of aromatic amines, phenols and dialkyl hydroxyl amines. Furthermore, the method to inhibit the increasing viscosity of hydrocarbon, e.g. in a bottom section of a tower, may be accomplished by adding the hydrocarbon viscosity inhibitor to the feed oil, reflux oil or directly to the tower bottom oil in the tower. Such an oil quench tower is used for an olefin production process in which the hydrocarbon may include naphtha, light oil, natural gas, liquefied natural gas, etc. in the raw material.