This thesis presents the results of an analysis of the effect of changes in the mean volume fraction and local volume fraction have on the drag force in flow past a fixed assembly of spheres. Current drag correlations address the mean drag of the system, but neglect changes in the mean and local volume fraction which could affect the flow more locally. The impact to the local drag and mean system drag, from local and mean volume fraction changes respectively, are compared. This is done by finding the predicted change in mean drag force as the mean volume fraction of the system changes for a variety of drag laws and comparing it with data from simulations in which the local drag and volume fraction fluctuations can be extracted. These simulations were previously performed using the PUReIBM method. It will be shown the local drag does not show a clear correlation in regard to local volume fraction changes. Furthermore, it will be seen the local drag fluctuations are negligible compared to the mean drag changes from a mean volume fraction change in the system.