Since the Texas Commission on Environmental Quality has determined that the Eagle Ford and its supporting industry will be included in future air emission inventories, it is crucial that the most accurate and cost effective methods for determining air emissions of drilling operations be identified. Estimation is the preferred method for creating regional emission inventories since direct measurement of diesel engine exhaust is often cost prohibitive. These estimations are commonly calculated using engine load, conservatively estimated at 100%. This introduces considerable error in the emissions inventory since electric rigs are rarely run at full load and drilling operators do not record engine activity. Conducting an air emission inventory of drilling rigs requires a novel way to estimate emissions without relying on engine load as a primary variable. With this in mind the research team employed an estimation method based on fuel consumption rather than horsepower. Fuel use data is readily available on drilling sites and so more accurately reflects the engine activity of electric rigs in drilling operations. This study finds that emissions calculated using different estimation methods can vary from 9 to 106 pounds per hour of NOx, but that the fuel consumption method offers an opportunity for more accurate assessment of regional emission inventories.