  We determine the accuracy of various approximations to the O(alpha)
corrections for on-shell W-pair production. While an approximation based on the
universal corrections arising from initial-state radiation, from the running of
alpha, and from corrections proportional to m_t^2 fails in the Linear-Collider
energy range, a high-energy approximation improved by the exact universal
corrections is sufficiently good above about 500GeV. These results indicate
that in Monte Carlo event generators for off-shell W-pair production the
incorporation of the universal corrections is not sufficient and more
corrections should be included.
