The report summarizes an investigation of the performance of commercial low-NOx burners in refinery process heaters. Refineries in Southern and Central California were surveyed to determine the number of existing or planned low-NOx burners. Tests on 10 process heaters equipped with low NOx burners measured gaseous emissions, particulates, and efficiencies at normal operating conditions. As-found NOx emissions increased from 58 to 245 ng/J as fuel-bound nitrogen increased from zero to 0.81%. In most cases, NOx concentrations were strongly influenced by excess air levels. Reducing excess air to 3-4% reduced NOx to 34-200 ng/J, depending on fuel nitrogen. Comparisons of present emissions data with past field test data for refinery heaters equipped with standard burners showed that (for mechanical-draft gas-fired heaters) low-NOx burners may reduce the NOx emission factor by 32-77% below the mean emission factor for standard burners. Three heaters (one firing gas; one, distillate oil; and one, residual oil) were selected as the most suitable candidates for 30-day continuous monitoring of gaseous emissions.