The report gives results of Phase II of a field study to assess the applicability of combustion modification (CM) techniques to control NOx and other pollutant emissions from utility boilers and gas turbines without causing deleterious side effects. Comprehensive, statistically designed tests were used to evaluate the effect of CM. The most extensively studied CM for utility boilers was staged firing at low excess air, which can reduce NOx emissions by up to about 50%, based on results of short-term tests. Tests of B and W's low-NOx, dual-fired utility boilers, special attention was paid to the determination of potentially adverse side effects: increased combustible emissions, unwanted changes in particulate mass loading and size distribution, reduced boiler efficiency, increased furnace slagging, and tube wall corrosion. Short-term tests indicate that staged combustion may be applied to coal-fired utility boilers. The extent of furnace tube wall corrosion and slagging could not be determined conclusively, based on results of short-term (300-hour) corrosion probing runs under low NOx and baseline operating conditions. It was found, however, that corrosion probes exposed for longer periods (300-1000 hours) may more effectively correlate with actual furnace tube corrosion rates.