Aniline point is an indicator of chemical composition of motor gasoline and diesel fuel and of their aromatic and paraffinic contents in particular. A significant relationship between the research octane number of unleaded motor gasoline and its aniline point was investigated. This relationship was evident in particular in the case of aromatic and naphthenic compounds with higher octane numbers. A correlation equation with a correlation coefficient of 95% was found with an acceptable average error.