The structure and soot formation characteristics of a coflow laminar methane/air diffusion flame under conditions of constant p2g and mass flow rates of the air and fuel streams were numerically investigated in order to examine the validity of the p2g scaling relationship. The p 2g scaling relationship has been used to experimentally investigate soot formation in weakly-buoyant laminar diffusion flames by conducting experiments at reduced pressures. Detailed numerical calculations were conducted by solving the elliptic conservation equations of mass, momentum, species, and energy in axisymmetric cylindrical coordinates using a standard control volume method. Detailed multi-component thermal and transport properties and detail combustion chemistry were employed in the modelling. Soot formation was modeled using a semi-empirical acetylene based model in which two transport equations for the soot mass fraction and soot number density per unit mass were solved. Thermal radiation was calculated using the discrete-ordinates method and a 9-band non-grey model for the radiative properties of the CO-CO 2-H2O-Soot mixture. The flame structure and soot formation characteristics exhibit strong dependence on the ambient pressure even though p2g and the mass flow rates are kept constant. Significantly more soot is produced with increasing the pressure and decreasing the gravity level. Numerical results clearly demonstrate that the p2g scaling relationship is invalid as far as soot formation is concerned.