The classification of the hydrodynamical growth mechanisms for the spherical bubbles of the low-temperature phase in cosmological phase transitions is completed by showing that the bubbles can grow as supersonic deflagrations. Such deflagrations consist of a Jouguet deflagration, followed by a rarefaction wave. Depending on the amount of supercooling, the maximal velocity of supersonic deflagrations varies between the sound and the light velocities. The solutions faster than supersonic deflagrations are weak detonations.

8 pages, RevTeX, 6 figures. Complete paper appended as uuencoded postscript and at http://www.physics.helsinki.fi/tft/tft_preprints.html