The report concerns a study to develop a pilot field-test program to evaluate combustion modification techniques to reduce NOx emissions from tangentially coal-fired steam-generating units. The report includes details of the preliminary test program, including analytical measurement and sampling techniques, engineering drawings, cost estimates, and schedules. Overfire air is the least expensive technique for controlling NOx, incurring no loss in unit efficiency or increased operating expenses. Flue gas recirculation is significantly more costly, requires additional fan power, and (in existing units) could result in a 10-20% decrease in load capability due to increased gas flow weights. Water injection into the fuel-firing zone has the lowest initial equipment cost; however, losses in unit efficiency (resulting in increased fuel costs and significant water consumption) make it the most expensive system to operate. The cost of applying controls to existing units generally is twice that of new units. (Modified author abstract)