High-temperature oxidation is one of the most promising technologies to reduce pollutants in combustion systems. The optimization of high-temperature oxidation is very complex, but has many advantages in the suppression of the thermal NO formation even at relatively high temperatures. The present study is based on parametric simulations of non-premixed counter-flow flames of methane with nitrogen dilution and highly preheated air. The objective of this study is to understand the effects of fuel dilution and strain rate on reaction zone structure and NOx formation in flameless combustion. This study shows that NOx mass fractions decrease with an increasing strain rate as well as increasing methane dilution with nitrogen.