The stability of the Y2Ba4Cu7Ox phase (Y-247) has been investigated under pure oxygen pressures up to 1700 bar. The samples, as synthesized at 1000°C and p(O2)=20 bar, show a critical temperature Tonsetc of 94K. However, the positive temperature derivative of the normal state susceptibility above the fluctuation region suggests that the optimum hole doping is not yet reached. Although at temperature higher than 600°C and p(O2) in the 1500 bar range, the 247 phase decomposes into YBa2Cu4O8 as a major phase, the metastable 247 phase may be further oxygenated at lower temperatures. The effect on the susceptibility is as expected (χ becomes temperature independent) but surprisingly, Tc saturates at 95K . Very long annealing times broaden the superconducting transition, decrease the Meissner fraction and finally induce decomposition even at temperatures as low as 300°C.