Electrospinning is a method to produce submicron polymer fibers for a wide range of applications and it is desirable to understand what determines the fiber diameter distribution in this process. A well instrumented and machine vision based system had been developed to provide the measurement capability for this study. This paper investigated several important process variation factors as well as the operating conditions which resulted in minimal Taylor cone and jet fluctuations. It was found that the dynamic variations of Taylor cone volume, electric current, and charge density correlated to the resulting fiber diameter distributions. Published by Elsevier B.V.