The impact of NOx reduction technologies upon a supercritical coal fired p.f. power station has been investigated using the ECLLPSE process simulator. Technical, environmental and economic assessments were performed, based upon a model of the Amer 9 Power Station at Geertruidenberg, the Netherlands. Selective catalytic reduction (s.c.r.) achieves the largest reduction in NOx emissions to below 50 mg/N m(3) but at an additional electricity cost of 0.21 p/kWh, over the base case. The additional cost for coal-over-coal reburning is 0.03 p/kWh, reducing NOx emissions to below 200 mg/N m(3). Only high unburnt carbon losses or high priced reburn coal justify the use of a coal microniser. Natural gas-over-coal reburning requires an unrealisable natural gas price of pound 0.98/GJ to compete with coal-over-coal reburning. Gas prices between pound 1.76/GJ and pound 1.93/GJ are required for it to compete with s.c.r.