The statistical correlation between a pair of electrons in Hartree-Fock orbitals is measured by mutual information and studied in position and in momentum space. We show that there are same-and opposite-spin orbital pairs where the correlation is larger in momentum space. Among these are opposite-spin valence shell pairs where the correlation arises from the indistinguishability of electron spins. (C) 2011 Elsevier B. V. All rights reserved.