Synchrotron radiation-excited photoelectron spectra (SRXPS) were used in order to elucidate flotation-related problems arising from adsorption of sulphur-containing heterocyclic collectors like 2-mercaptobenzothiazole (MBT) on galena. MBT is considered to be representative for a new group of selective collectors for flotation of sulphide minerals. SRXPS provides a strongly enhanced surface sensitivity compared to conventional XPS. A further advantage is the increased excitation cross-section of S compared to Pb which allows the extraction of quantitative results from the S2p spectra of the adsorbates. Additional components besides the signal of the bulk sulphide were observed in the S2p spectra of cleaved as well as preoxidized galena samples proving the chemisorption of MBT and the multilayer formation of oxidation products. Using the intensity ratios of adsorbates vs. bulk signals in dependence on the adsorption conditions, a model is developed for the composition and the structure of the overlayer.