The vapor pressure of H2SO4 over 98.01 mass-% sulfuric acid solution has ben determined experimentally over the temperature interval 338 to 445 K. values of the enthakpy and entropy changes upon vaporization deduced from the data accord well with other estimates available in the literature. Extrapolation to 99.0 mass-% and 296.15 K allows us to confirm another recent vapor pressure determination, thereby supporting the conclusion that the vapor pressures most often used in nucleation calculations in the past are as much as an order of magnitude high.