Simplified versions of CBS‐QB3 model chemistry were used to calculate the free energies of 36 deprotonation reactions in the gas phase. The best such version, S9, excluded coupled cluster calculation [CCSD(T)], and empirical (ΔEemp) and spin‐orbit (ΔEint) correction terms. The mean absolute deviation and root mean square thus obtained (viz. 1.24 and 1.56 kcal/mol, respectively) were very‐close to those provided by the original CBS‐QB3 method (1.19 and 1.52 kcal/mol, respectively). The high‐accuracy of the proposed simplification and its computational expeditiousness make it an excellent choice for energy calculations on gas‐phase deprotonation reactions in complex systems. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010