A simplified method is shown, based on a semi-empirical procedure, to estimate the detonation velocities of CHNO explosives at various loading densities. It is assumed that the product composition consists almost of CO, CO2, H2O and N-2 for oxygen-rich explosives. In addition solid carbon and H-2 are also counted for an oxygen-lean explosive. The approximate detonation temperature, as a second needed parameter, can be calculated from the total heat capacity of the detonation products and the heat of formation of the explosive by PM3 procedure. The detonation velocities of some well-known CHNO explosives, calculated by the simple procedure, fit well with measured detonation velocities and the results from the well-established BKW-EOS computer code.