We have investigated the response to pressure of liquid SiO2 by performing a quantitatively realistic Monte Carlo simulation. The model liquid was restricted to at most four-fold Si-O coordination by the effective imposition of an infinite potential barrier to a fifth bond. We thus obtained an unambiguous comparison of the compression mechanisms of solid and liquid tetrahedral networks. In spite of this restriction, the density of the simulated liquid exceeds that of the corresponding models of quartz, coesite and cristobalite at high pressure. The efficient compression of the liquid results from a continuous restructuring of the network that leaves the mean Si-Si distance virtually unchanged and does not require an increase in the coordination number. The restructuring is effected by local breaking and reconnecting of bonds, a mechanism that is not available to a perfect crystal. ¿ American Geophysical Union 1989