Surface oxidation of samples from vitrain bands (low mineral content) in two Australian bituminous coals (Greta and Whybrow seams, Sydney Basin, NSW) were studied following thermal treatment in air at temperatures ranging from 20 degrees C to 120 degrees C for periods of up to 370 days. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) studies indicate clear changes in oxygen function group concentration at the surface of coal organic matter under different atmospheric oxidation conditions. The oxidation products observed include hydroxyl groups or ether linkages, carbonyl groups, and carboxyl groups. Increases in oxidation temperature accelerate the process of carboxyl group formation. It is found that the surface concentration of carboxyl groups can be used as an indicator of the extent of oxidation in low sulfur-content bituminous coals. This may be useful in coal preparation research.