A method of providing a suitable candidate liquid for an electrospray system is provided. At a first step an aperture radius for an aperture of the electrospray system (10) through which the liquid to be electrosprayed is drawn is obtained. Next, a corona threshold electric field curve as a function of relative permittivities of candidate liquids is calculated to determine the electric field at which undesirable corona discharge will occur. The maximum surface tension that can be electrosprayed by the system is calculated and then a candidate liquid which has a chosen relative permittivity and a surface tension that is equal to or less than the maximum surface tension is provided, to thereby provide a suitable candidate liquid with an appropriate surface tension to result in electrospray that meets the requirements of the electrospray system.