An important source of benzol is coke oven gas, which is a by-product of metallurgical coke production. A cycle of absorption into the washing oil and reverse desorption is a crucial step in this technology. The wash oil itself is a complex mixture of hydrocarbons with higher boiling point. Its washing property is changing during time of use. The concentration of unabsorbed benzene in the coke oven gas leaving the absorption is monitored as an indicator of the washing oil condition. A secondary parameter is the viscosity of the washing oil. The optimal operating conditions of the absorption unit of benzol and the ranges of physical properties, which mainly influence the benzol absorption, were identified. Beside the increasing absorption efficiency, it is significant to prolong the life cycle of wash oil.