Surface analysis is made by nuclear, non-destructive, means and computer simulation for the energy method of analysis. The predicted energy spectra are compared to experimental data, giving target composition and concentration profile information. Mainly, target parameterization and available nuclear data are considered in the computations. The method is favourably applied to the determination of an 18O step concentration profile in a thick oxidized target. A uniform concentration profile of 12C is found for a thick target. Elastic scattering permits depth profiling of Al and O in a thick oxide target.