  Based on a high temperature expansion, we compute the two-point correlation
function and the critical line of an Ising lattice gas driven into a
non-equilibrium steady state by a uniform bias E. The lowest nontrivial order
already reproduces the key features, i.e., the discontinuity singularity of the
structure factor and the (qualitative) E-dependence of the critical line. Our
approach is easily generalized to other non-equilibrium lattice models and
provides a simple analytic tool for the study of the high temperature phase and
its boundaries.
