We present the O(as^4) virtual QCD corrections to unlike-quark and like-quark
scattering due to the interference of one-loop amplitudes with one-loop
amplitudes. The structure of the infrared divergences agrees with that
predicted by Catani. The results are expressed in an analytic form so that the
relevant expressions for crossed scattering processes can be obtained in a
straightforward manner. The one-loop contributions presented here, together
with the interference of tree with two-loop amplitudes given recently, complete
the 2 to 2 virtual QCD corrections at NNLO for the massless quark scattering
processes.Comment: 11 pages, LaTeX using JHEP.cl