The report gives results of analyzing long-term nitrogen oxide (NOx) emission data from eight pulverized-coal-fired steam generators, for the purpose of quantifying the effectiveness of various combustion modifications. All boilers, but one, were modified to reduce NOx emissions. The modifications included changing both hardware and operating procedures. All boilers were subject to the NOx provisions of the 1971 New Source Performance Standards (NSPS). In several instances, when long-term emission data for the period before the modification were not available, the quantification of the NOx reduction was based on the result of the performance test required by the 1971 NSPS. NOx reductions of from 5.1 to 60% were determined without incurring significant adverse impacts on unit operation. NOx emission levels, determined from the performance tests, were from 146 to 473 ng/J (0.34 to 1.10 lb/million Btu) before control implementation, and from 148 to 281 ng/J (0.34 to 0.65 lb/million Btu) after combustion modifications were applied.