Atomic absorption spectroscopy is widely used to determine worn metals in used multigrade oils, especially iron and copper. It has been found that measurement of iron and copper are subjected to matrix interferences from viscosity index improvers presented in the multigrade oil formulations. Such interferences are related to the chemical structure and concentration of the incorporated viscosity index improver. This study is aimed at establishing regression equations for some commercial viscosity index improvers, so that these equations can be used in correction for measured concentrations of iron and copper in used multigrade oils.