This paper deals with the identification of reaction and mass-transfer rates from concentrations measured in gas-liquid reaction systems. It is assumed that the reactions take place in the liquid bulk only. The identification proceeds in two steps: (i) estimation of the extents of reaction and mass transfer from concentration measurements, and (ii) estimation of the parameters of the individual reaction and mass-transfer rates from the extents. For the estimation of the individual extents, two cases are considered: if the concentrations of all the species in the liquid phase can be measured, a linear transformation is used; otherwise, if the concentrations of only subsets of the species can be measured in the gas and liquid phases, an approach as an extension of the linear transformation is proposed. The approach is illustrated in simulation via the chlorination of butanoic acid.