  Disk instability is an attractive yet controversial means for the rapid
formation of giant planets in our solar system and elsewhere. Recent concerns
regarding the first adiabatic exponent of molecular hydrogen gas are addressed
and shown not to lead to spurious clump formation in the author's disk
instability models. A number of disk instability models have been calculated in
order to further test the robustness of the mechanism, exploring the effects of
changing the pressure equation of state, the vertical temperature profile, and
other parameters affecting the temperature distribution. Possible reasons for
differences in results obtained by other workers are discussed. Disk
instability remains as a plausible formation mechanism for giant planets.
