The syntheses of several ternary platinum oxides are reported. The Na and Cd bronzes NaxPt3O4 and CdxPt3O4 as well as the bronze-like CaPt2O4 were prepared in powder form under atmospheric pressure. The existence of Pt3O4 is discussed. Syntheses for CdxPt3O6 and a poorly defined new simple oxide of platinum with stoichiometry Pt5O6 are given. The stability of these various oxides is discussed and their lattice parameters are given. The crystal chemistry of these oxides is systematized using stability fields for the platinum bronzes and for A3BX4 compounds. The close structural relationship between the bronzes and Ag3PO4 and Ag3AsO4 is discussed. Photoelectron spectroscopic, magnetic susceptibility, and electrical conductivity data for the bronzes and various other platinum oxides are reported. From these data it is concluded that most bronzes are metallic oxides and a qualitative one-electron energy-band scheme is given explaining this metallic character. The nonexistence of CaPt3O4 is discussed in terms of both this scheme and thermodynamics. The tendency of the bronzes to incorporate large quantities of foreign cations is explained in terms of the cage-like bronze structure.