  We develop a formalism for general relativistic, grand canonical ensembles in
space-times with timelike Killing fields. Using that formalism we derive ideal
gas laws, and show how they depend on the geometry of the particular
space-times. A systematic method for calculating Newtonian limits is given for
a class of these space-times, which is illustrated for Kerr space-time. In
addition, we prove uniqueness of the infinite volume Gibbs measure, and absence
of phase transitions for a class of interaction potentials in anti-de Sitter
space-time.
