The reactive chemisorption of three organophosphorus compounds have been investigated at clean and oxidised Al(1 1 1) surfaces using X-ray photoelectron spectroscopy (XPS). Phosphoric acid, trimethyl ester (or trimethylphosphate, TMP, O=P(OCH3)(3)), and methyl phosphonic acid and dimethyl ester (or dimethylmethylphosphate, DMMP, O=P(CH3)(OCH3)(2,)) were adsorbed from the gas phase, but this approach proved unsuccessful for methyl phosphonic acid (MPA, O=P(CH3)(OH)2) due to decomposition in the gas phase. NIPA was therefore adsorbed from either an aqueous or an ether solution placed onto the aluminium. sample in a helium atmosphere. Core binding energies for the P-OCH3, P-CH3, P-O and P=O groups are reported and the decomposition pathways for the three compounds discussed, The P-CH3 bond is stable at both clean and oxidised aluminium surfaces up to temperatures of 570 K, whereas the P-OCH3 bond can be broken even at room temperature. Decomposition of all three molecules requires clean aluminium sites and is hindered by high concentrations of adsorbed species.