The effect of reagent molar ratio and temperature upon the composition of oxyethylated fatty acid methyl esters and surface tension reduction at air/water interfaces was studied. It was found that oxyethylation of fatty acid methyl esters carried out in the presence of calcium-based catalyst gives narrow range distributed products. The distribution depends on temperature, and more narrow products are obtained at higher temperatures. Oxyethylated fatty acid methyl esters contain less unreacted hydrophobic starter than oxyethylated alcohols. The pressure drop in the batch process can be satisfactorily modeled, assuming the reaction proceeds in the liquid phase and estimating the concentration of the ethylene oxide in the liquid phase from vapor-liquid equilibrium. The modeling supports the important role of ethylene oxide diffusion from the gas to the liquid phase. The distribution of the polyoxyethylene chain in hydrophilic oxyethylated fatty acid methyl esters has only a minor effect upon the surface tension reduction and the values of characteristic adsorption coefficients. The effect of the synthesis temperature is not reflected in the surface tension reduction.