This paper presents the findings from a study on the evaporation process of 93 RON (research octane number) unleaded gasoline. The parameters measured in the experiment included the weight, the RVP (Reid vapor pressure) and the viscosity of gasoline, the concentration of NMHC (non-methane total hydrocarbon) in the oil vapor and the concentration of the main vapor constituent. Results showed that the parameters changed significantly as evaporation processed. The weight loss reached 86.36% after 300 days and presented a logarithmic curve with time. The RVP decreased from 38 kPa to 9.6 kPa. The viscosity of gasoline increased from 8.6 x 10(-4) Pa s to 1.51 x 10(-3) Pa s. All the concentrations of NMHC and the main constituent of vapor decreased in varying amounts. Most of the changes might be attributed to the evaporation of volatile hydrocarbons. (c) 2012 Elsevier Ltd. All rights reserved.