  We evaluate the neutrino nucleon charged current cross section at
next-to-leading order in quantum chromodynamic corrections in the variable
flavor number scheme and the fixed flavor number scheme, taking into account
quark masses. The number scheme dependence is largest at the highest energies
considered here, $10^{12}$ GeV, where the cross sections differ by
approximately 15 percent. We illustrate the numerical implications of the
inconsistent application of the fixed flavor number scheme.
