For engineering calculations in the gas phase, correlatsons have been established between smoke point heights and heat of combustion and yields of CO and particulates. Smoke point heights reported in the literature were modified such that all the data, including those measured by us, were consistent. Based on the data for 165 fuels from the literature and the data measured by us for 16 fuels, relationships have been suggested for the engineering calculations of heat of complete combustion, chemical heat of combustion and its convective and radiative components, and yields of CO and particulates as functions of the molecular weight for fuels with aliphatic and aromatic, saturated and unsaturated bonds between C and H; C, H and O; C, H, N and C, H and S atoms. The efficiency of combustion decreases with increase in the bond unsaturation and aromatic nature. Substitution of O atoms in the structure increases the efficiency of combustion, where as substitution of N and S atoms in the structures decreases the efficiency of combustion, S atoms being more efficient than N atoms. The generalized relationships have been used to assess the decomposition, gasification and combustion processes for polymers.