Results arts presented from ab initio quantum chemical calculations on the ground-state potential energy surface for the open shell doublet reaction: HNO + NO --> N2O + OH (reaction I). This reaction is thought to be important in the sustained combustion of nitrogen-containing fuels. Geometry optimizations have been carried out at the QCISD/6-31G(d,p) level using unrestricted Hartree-Fock zeroth-order wave functions in search of local minima and transition states, followed by energy refinements for ail critical points at the QCISD(T)/6-311+G(2df,2p) level. All saddle points were subjected to intrinsic reaction coordinate calculations to determine tile minima to which they connect. We report two completed reaction pathways for reaction I, Some of these results will be compared with earlier work by others on the same reaction where geometry optimizations were carried out primarily at the UMP2/6-311G(d,p) level, The comparison brings to light some interesting differences between QCISD and UMP2 theories in the prediction of molecular structures and the connectivity of critical points (and therefore, connected reaction paths) for the doublet system in reaction I.