Diesel and jet engines often operate at elevated pressures, thus the investigation of the effect of pressure on soot nanostructure may contribute to the understanding of real-world systems. In this paper preliminary results from the analysis of soot nanostructure as a function of oxidation pressure are presented. The analyzed soot was generated in premixed flames of liquid fuels: n-dodecane, m-xylene and n-butanol and oxidized under elevated pressures. Nanostructure is described via differentiating between the isotropic and nematic phases of soot particles. These phases are characterized by the polar and nematic order parameters. Along with the order parameters, the nematic phase is further characterized by graphene layer spacing and length. The structural parameters were measured by utilizing high-resolution electron microscopy and digital image analysis. The image analysis framework used in this paper is a recent development, that provided us with high-fidelity structural data. This refined methodology made drawing our conclusions possible. A significant effect of pressure was observed on soot nanostructure - increasing pressure reduced interlayer spacing and increased the average length of layers, along with altering the symmetries of the structure.