Microbubble floating in liquid dielectric and subjected to an electric field may initiate partial discharge (PD). This paper studies the parameters that affect the initiation through a computer simulation. This study inspects how the type of gas inside the microbubble, the size of the microbubble, distance from an electric field, Eo, source and, the magnitude of source’s voltage affect the start of PD. For a prolate spheroid shape, there is an important parameter called ‘c’. This ratio is between the radius of the microbubble polar (‘a’) and the radius of the equator (‘b’). At constant Eo and c, different gases will initiate PD at different distances from source due to differences in a localised electric field inside the microbubble (Emax). Emax is one of the important factors for PD initiation. It is interesting to report that if the ‘a’ and ‘b’ values are chosen so that ‘c’ will be constant, changes in Emax are insignificant. On the other hand, changes in ‘c’ will result in significant changes in Emax. Finally, changes in source’s voltage certainly affect the Emax.