Droplet formation from capillary streams of viscous low vapor pressure fluids in a vacuum has been studied. A new form of capillary stream breakup, which entails the use of an amplitude‐modulated sinusoidal disturbance, has been employed extensively in this work. The genesis of droplets formed due to an amplitude‐modulated disturbance on a stream is reviewed in some detail and illustrated pictorially. Because capillary stream breakup and subsequent droplet propagation took place in a vacuum there were no significant interactions with the surrounding atmosphere. Sensitive measurements of the relative speeds of each drop have been made by allowing them to travel 6 m in a vertical vacuum chamber, and measuring the time between drops using an optical method. Speed differences as low as 3.5×10−7times the average stream speed have been measured. New information about capillary stream breakup is inferred by comparing the speed variations for droplet streams generated with both amplitude‐modulated disturbances and single‐frequency disturbances. An autoregressive model is developed and found to represent the deviations in time between droplets with consistency and reproducibility.