The breakup of a laminar liquid jet is the underling phenomena used to generate emulsions in micro-scale devices. Jet breakup is induced by the most unstable disturbance growing on the jet surface, and linear instability analysis can be utilised to predict the resultant droplet size. Previously, instability analysis has been applied to stationary jets only. This study investigates the influence of the jet velocity on the jet breakup for a water-in-oil system. The breakup of moving water jets were monitored using a high speed camera. The resultant droplet sizes were strongly influenced by jet velocity. A linear analysis for a moving jet was developed to determine the most unstable disturbance and the resultant droplet size. It was found that the new (moving) model can provide better prediction than the available stationary model. The modelling results can also quantify the limiting velocity for linear instability analysis.