It is important to understand the initial stages of oxygen adsorption and reaction on alpha-silicon because of its importance in the development of nanometre silicon-based microelectronic devices. This was achieved effectively using precise background corrections applied to Si 2p x-ray photoelectron spectroscopy (XPS) measurements based on effective energy-loss functions derived from reflection election energy-loss spectroscopy analysis. It was also essential to determine O 1s XPS source functions based on the optical bulk energy-loss function. Significant correlations between the chemical shifts of the Si 2p and O 1s XPS source functions with oxygen exposure using this approach were observed. It enabled us to develop a model for oxygen adsorption and reaction at oxygen exposures of 0-1000 L at room temperature from detailed analysis of the changes in the fine spectral features revealed by this analytical approach. Features of the application of this procedure are illustrated in this paper and its application to developing a coherent understanding of the initial stages of oxygen adsorption and reaction on alpha-Si at room temperature is reported.