The report gives results of subscale tests to evaluate combustion modifications for emission control on petroleum process heaters, cement kilns, and steel furnaces. The aim was to assess applicability, NOx emissions reductions, and cost effectiveness of several modifications and to select the most promising for pilot scale tests. Subscale process heater baseline NOx were about 55 ng/J firing natural gas at 2.9 MW heat input. NOx were reduced by 67% with staged combustion and by 63% with flue gas recirculation (FGR). Firing No. 6 oil, baseline NOx of 160 ng/J were reduced by 51% with staged combustion and by 39% with FGR. Staged combustion was selected for pilot scale tests. Subscale cement kiln, baseline NOx were 30-60 ng/J firing natural gas at about 80 kW heat input. Fly ash, kiln dust, water, and sulfur were injected separately to evaluate the NOx reduction potential. Fly ash injection reduced NOx by 28%; the other injectants reduced NOx by 12-20%. Further work at a larger scale is planned prior to selecting modifications for pilot scale tests. For the subscale steel furnace, baseline NOx of 115 ng/J firing natural gas at 0.6 MW heat input were reduced by 88% with FGR and by 47% with water injection. Firing No. 2 oil, baseline NOx of 160 ng/J were reduced by 77% with FGR and by 89% with steam injection.