Electrical conductivity measurements were carried out on pure crystalline GeO2 at pressures up to 4.2 GPa and temperatures up to 1273 K through the alpha-quartz to rutile structural transformation. The T-1 dependence of the conductivity shows two distinct regions : at all P investigated, the activation energy, Q(c), varies in the range 0.03 to 0.08 eV for T < 673 K whereas in the high T region, Q(c) is more than an order of magnitude higher in the range of 0.58 to 3.46 eV. The P dependence of the conductivity also changes significantly between the low and high T regions, with a negative activation volume, Delta Y double dagger, at low T and a positive Delta V double dagger at high T. The contrasting P dependence of the conductivity in the low and high temperature regions suggests a reversible thermally-activated change in conduction mechanism, from low T electronic to high T ionic.