Pb2Re2O7-xhave been synthesized in sealed evacuated silica tubes by a high-pressure, high-temperature technique. The products were characterized by X-ray powder and single-crystal diffraction, electron diffraction, energy-dispersive X-ray analysis, and thermogravimetric analysis. Anion-deficient pyrochlore-type structures of Pb2Re2O6.65and Pb2Re2O6.75were refined from X-ray powder data (a=10.4314(1) Å, space groupFd3m,RI=0.027,Rp=0.055) and single-crystal data (a=10.4239(3) Å, space groupFd3m,RF=0.025,Rw=0.036), respectively. Electron diffraction of the Pb2Re2O6.65oxide revealed a superstructure corresponding to a possible space groupP3m1 with cell parametersah=ac/2≈7.39 Å andch=2ac3≈36.20 Å. A high-pressure-induced phase transition between the Pb2Re2O7-xpyrochlore and the Pb6Re6O19compound was found.