Labeled hydrogen-filled graphs (LHFGs) together with graphs of atomic orbitals (GAOs) have been used to represent the molecular structure of alkanes. The GAO is an attempt at taking into account the structures of atoms (i.e., atomic orbitals such as, 1s(1), 2p(2), 3d(10)) for QSPR/QSAR analyses. As a method of alkane enthalpies modeling, optimization of correlation weights of local invariants (OCWLI) of the LHFGs and the GAOs has been used. Statistical characteristics of such models based on the OCWLI of the GAO are better than those based on the OCWLI of the LHFGs. (C) 2003 Elsevier B.V. All rights reserved.