The design of a reliable low-NOx burner requires a good understanding of the mixing between the fuel and air jets. This is true both for technologies using staging of the combustion air and for those using exhaust gas recirculation. Therefore, there is a need for detailed measurements in the near-burner region to validate the theories on which the burner technology is based and to better understand the processes involved in this region of the furnace. This article presents intrusive measurements of conventional combustion products (O-2, CO2, CO, and NOx) and mean and fluctuating components of temperature using a laser-based measurement system (CARS) in two natural gas flames produced by two commercially available burners. Based on these measurements, the burners are compared with respect to combustion performance. The low-NOx burner produced similar amounts of NOx compared to the other burner. The reason for this is found in the differences in the fluctuating component of gas temperature in the flames from these burners. The low-NOx burner is shown to have broad temperature profiles resulting in much larger regions where the temperature is above the 1800 K limit for NOx formation compared to the high-NOx burner.