Existence, uniqueness and stability of solutions is studied for a set of nonlinear fixed point equations which define self-consistent hydrostatic equilibria of a classical continuum fluid that is confined inside a container Λ ⊂ R 3 and in contact with either a heat and a matter reservoir, or just a heat reservoir. The local thermodynamics is furnished by the statistical mechanics of a system of hard balls, in the approximation of Carnahan-Starling. The fluid's local chemical potential per particle at r ∈ Λ is the sum of the matter reservoir's contribution and a self contribution −(V * ρ)(r), where ρ is the fluid density function and V a non-negative linear combination of the Newton kernel V N (|r|) = −|r| −1 , the Yukawa kernel V Y (|r|) = −|r| −1 e −κ|r| , and a van der Waals kernel V W (|r|) = −(1 + κ 2 |r| 2 ) −3 . The fixed point equations involving the Yukawa and Newton kernels are equivalent to semilinear elliptic PDEs of second order with a nonlinear, nonlocal boundary condition. We prove the existence of a grand canonical phase transition, and of a petit canonical phase transition which is embedded in the former. The proofs suggest that, except for boundary layers, the grand canonical transition is of the type "all gas ↔ all liquid" while the petit canonical one is of the type "all vapor ↔ liquid drop with vapor atmosphere." The latter proof in particular suggests the existence of solutions with interface structure which compromise between the all-liquid and all-gas density solutions.