We use a combination of molecular orbital theory and our generalized Keldysh theory to theoretically study tunneling photo-ionizations of neutral ethylene and benzene molecules in high-power linearly polarized Ti:sapphire laser fields (800 nm). We consider the ionization from the highest occupied molecular orbital of the ground electronic state, and show that molecular ionizations consist of the individual ionizations from each atom and the quantum interferences between them. We clarify the effects of the quantum interferences on the tunneling photo-ionizations of molecules. Our theoretical results agree well with experimental data and other theoretical results. (c) 2006 Elsevier B.V. All rights reserved.