This research demonstrated the ability of a Computational Fluid Dynamics (CFD) modeling approach to predict the severity of velocity profile disturbances in two different header configurations with AGA-9 default meter runs. The CFD model was also used to predict the flow measurement error based on the ultrasonic path geometry from four commercially-available ultrasonic flow meters. In addition to the CFD modeling, this project experimentally tested the same two header configurations in a natural gas flow loop. The results from the experimental testing were used to validate the CFD model.