For an O͑N͒-symmetric scalar field theory with Euclidean action ͐d 3 x ͓ 1 2 ͉ ٌ ͉ 2 + 1 2 r 2 + 1 4! u 4 ͔ , where = ͑ 1 , . . . , N ͒ is a vector of N real-field components, variational perturbation theory through seven loops is employed for N =0,1,2,3,4 to compute the renormalized value of r / ͑N +2͒u 2 at the phase transition. Its exact large-N limit is determined as well. We also extend an earlier computation of the interaction-induced shift ⌬͗ 2 ͘ / Nu from N =1,2,4 to N =0,3. For N = 2, the results for the two quantities are used to compute the second-order shift of the condensation temperature of a dilute Bose gas, both in the homogenous case and for the wide limit of a harmonic trap. Our results are in agreement with earlier Monte Carlo simulations for N =1,2,4. The Appendix contains previously unpublished numerical seven-loop data.