AbstractA test set of 65 hydrocarbons was examined to elucidate theoretically their thermodynamic properties by performing the density‐functional theory (DFT) and ab initio calculations. All the calculated data were modified using a three‐parameter calibration equation and the least‐squares approach, to determine accurately enthalpies of formation (ΔHf), entropies (S), and heat capacities (Cp). Calculation results demonstrated that the atomization energies of all compounds exhibited an average absolute relative error ranging between 0.11– 0.13%, and an ΔHf of formation with a mean absolute absolute error (M.|A.E.|) ranging from only 5.7–6.8 kJ/mol (1.3–1.6 kcal/mol) (i.e., those results correlated with those of Dr. Herndon's 1.1 kcal/mol). Additionally, the entropy ranged from 3.5–4.2 J/mol K (0.8–1.0 cal/mol K) M.|A.E.|; a heat capacity between 2.3–2.9 J/mol K (0.5–0.7 cal/mol K) M.|A.E.| was obtained as well. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 537–544, 2006