Fuel composition has a significant effect in emissions from particulate matter (PM) and soot formation in internal combustion engines. Numerous studies, both experimental and numerical, have reported that oxygenated fuels reduce particulate emissions. These studies have proved that this reduction depends not only on the oxygen content but also on the molecular structure and the different oxygen functional groups. Consequently, this paper contains an analysis of the relationship between fuel composition and soot formation and PM emissions from oxygenated fuel blends. In this study, ethanol-gasoline and biodiesel-diesel fuel blends have been tested via a smoke point lamp in order to determine the variations in the sooting tendency in relation to the oxygen content of fuel blends and the effect of oxygenated additives on the sooting propensity of the blends. Particulate matter collected from the smoke point tests has been analyzed via XRay Photoelectron Spectroscopy (XPS) to quantify the surface oxygen content of the soot samples and to qualitatively identify oxygen functionalities on the samples. An attempt was made to correlate these results with the oxygen concentrations and molecular structure of the fuels.