NOx emission indices (NOxEI) of laminar high-pressure and turbulent liquid-fueled partially premixed flames are studied as a function of fuel tube equivalence ratio Phi(B.) In both cases, NOxEI behavior appears to be affected by changes in soot production. Soot levels were visually observed to decrease with increasing levels of partial premixing (decreasing Phi(B)) The resulting Variation in NOxEI with Phi(B) is vastly different from the variation observed for flames with negligible soot. For the soot containing flames, NOxEI increases continuously with increasing levels of partial premixing. The increase in NOxEI becomes more rapid beyond the point at which soot formation is suppressed, with a subsequent sharp reduction in NOxEI for Phi(B).less than or equal to 1.3. Based on these results, we suggest that optimum level of partial premixing can be designed to eliminate soot formation without a steep NOxEI penalty in high-pressure flames.