The lowest five singlet potential energy surfaces in the entrance region for the O(D-1) insertion into a C-C bond in cyclopropane have been calculated at the CASPT2/cc-pVDZ level of theory. It was found that the lowest surface is attractive, while the other four are repulsive. For comparison, the lowest five singlet potential surfaces for the O(D-1) insertion into the C-C bond in ethane were calculated using the same theoretical method. All the surfaces were found to be repulsive in the entrance region. The computational results are consistent with recent experimental observations for the O(D-1) reaction with small alkane molecules. (C) 2002 Published by Elsevier Science B.V.