This paper reports on a detailed physical chemical characterization of different carbonaceous particulates (commercial carbon blacks and diesel engine-derived soot) by using a combination of several techniques such as scanning electron microscopy (SEM), absorption isotherms, infrared spectroscopy, and small angle X-ray scattering (SAXS), to provide information on the chemical composition and structure at the micro- and nanoscale level. SEM micrographs indicate an almost spherical primary unit for all investigated samples with a diameter ranging from 5 to 100 nm. On the other hand, SAXS allows extracting the fractal dimension of both the primary units and the aggregates. All these results, taken together, can be used as a reference point to define an appropriate and rather cheap commercial surrogate for engine-derived soot and, alternatively, to choose the better carbon black according to the final industrial application.