The odd-order dispersion coefficients C-11, C-13, C-15 appearing in the third order of perturbation theory, and the even-order ones C-12, C-14, C-16 with contributions from the second and fourth order were calculated for binary interactions among helium atoms in the lowest singlet and triplet S states. The computations were carried out in the determinant based full configuration interaction approach using specially optimized Gaussian basis sets. The sum-over-pseudostates technique was employed to construct the reduced resolvent. The results of our calculations show a limited accuracy of the extrapolation formulas used thus far to compute these higher-order coefficients. (c) 2008 Elsevier B.V. All rights reserved.