  We present new methods for the evaluation of one-loop tensor integrals which
have been used in the calculation of the complete electroweak one-loop
corrections to e+ e- -> 4 fermions. The described methods for 3-point and
4-point integrals are, in particular, applicable in the case where the
conventional Passarino-Veltman reduction breaks down owing to the appearance of
Gram determinants in the denominator. One method consists of different variants
for expanding tensor coefficients about limits of vanishing Gram determinants
or other kinematical determinants, thereby reducing all tensor coefficients to
the usual scalar integrals. In a second method a specific tensor coefficient
with a logarithmic integrand is evaluated numerically, and the remaining
coefficients as well as the standard scalar integral are algebraically derived
from this coefficient. For 5-point tensor integrals, we give explicit formulas
that reduce the corresponding tensor coefficients to coefficients of 4-point
integrals with tensor rank reduced by one. Similar formulas are provided for
6-point functions, and the generalization to functions with more internal
propagators is straightforward. All the presented methods are also applicable
if infrared (soft or collinear) divergences are treated in dimensional
regularization or if mass parameters (for unstable particles) become complex.
