The kinetics of oxidation of acrolein on a commercial-type catalyst have been investigated in a tubular reactor, fitted with sampling devices. The dependence of gas-phase composition on residence time leads to a description of the kinetics by three independent reactions occurring in parallel or consecutively and their respective rate equations in a quantitative way. The interaction of these rate processes determines selectivity and yield of acrylic acid. The influence of temperature and gas-phase composition on the rates of individual reactions has been evaluated; water vapor is of foremost importance in this respect. Results are quantified by listing the rate coefficients and their dependence on external variables. A mathematical model of the kinetics in the two-stage process from propene to acrolein and from acrolein to acrylic acid can be obtained by combining the present results with those of a prior investigation concerning the partial oxidation of propene.