The vapor pressure of a series of edible oils (soybean oil, rape seed oil, cotton-seed oil, safflower oil, rice wax and sesami oil) were measured in a temperature range of 250℃ to 330℃ by using an assembly of U-tube mercury manometer and vacuum pump. It was tried to apply the Riedel’s type equation (Riedel, 1945a, b) to the measured results to obtain relationship between the vapor pressure and the temperature. The results obtained could be summarized, as follows : 1) The vapor pressure increased with increasing temperature. Soybean oil, rape seed oil, cotton-seed oil and rice was showed sigmoid curves which had a inflection point at about 290℃. In the case of Sesami oil the curve had the constant value in a range from 280℃ to 300℃. Only in safflower oil the curve showed simple exponential type. 2) Generally, vapor pressure estimates using the integral of the Clausius-Clapeyron’s equation assuming constant evaporation heat. But for these sigmoid type curves it is clear that such equation could ‘not express the curves. Thus the Riedel’s type equation with 4 parameters was introduced, the data of each oil were fitted to the equation by the leasts squares method as follows : In Pvp=A+B*T^<-1>+C.lnT+D*T^6 (3) The results agreed well with the experimental results and their standard deviations were in the range of 0.3026--0.9043kPa. The latent heat of evaporation could be estimated from eq. (3). Further, the other thermal characteristics were measured.
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