This work investigates in greater detail than in previous studies the effect of geometry on the relationship between emitted flow rate and applied potential difference in cone-jet mode electrospray systems. The magnitude of the flow rate to voltage relationship is demonstrated to be sensitive to numerous geometric parameters. An explanation of this variation is offered; it is demonstrated that in the cone-jet mode of operation the change of flow rate with the applied extraction voltage is due to the change in electric field at the tip of the emitter. By a finite element method simulation of the assumed electrostatic process the analysis is further extended to include all geometric parameters. The results outlined show the change of flow rate with applied voltage in cone-jet mode electrospray can be significant. This dependence will, under some conditions, have a considerable effect on the electrospray flow rate, and consequently current and droplet size. This has implications on electrospray applications involving the use of the applied voltage to extract the sprayed solution, including nano-electrospray mass spectrometry techniques and some forms of electrospinning. © 2012 American Institute of Physics.