  A general calculation of high pressure induced transition temperature (T c)
increases for oxide superconductors gives a good description for the
Hg-Ba-Ca-Cu-O system. Predictions are made of the maximum T^ cP theo =163, 154,
and 111K compared with T^ cP exp = 164, 154, and 118K respectively for the
superconducting phases of Hg-1223, Hg-1212, and Hg-1201 as a function of their
compressibilities agreeing with experiment. The theoretical result is in the
form of a universal scaling equation for the fractional change in T c as a
function of pressure, which is derived from a recent phenomenological theory of
short coherence length superconductivity.
