Thermodynamic calculations of graphite yield at the interaction of gaseous components of the C-H-O system were performed. Their results proved to be in satisfactory agreement with experimental data published on the lower concentration boundary of the diamond deposition region, The calculations indicate an influence of the substrate temperature, total pressure, and concentrations of inert and active additives on this boundary's location. These data confirm an inference that a diamond deposition mechanism might include spontaneous growth-etch cycles due to fluctuations of the gas concentrations. (C) 1996 American Institute of Physics.