A model has been produced which is an initial attempt to predict the effect of loading rate and other parameters on the propagation of a tensile crack in a fluid-saturated porous material under compression. The model is based on an existing treatment for a nonsaturated brittle solid but includes (in a simplified way) the influence of internal fluid pressure within the propagating crack and the way that this is changed by fluid flow into the crack. The predictions of the model are that at very low loading rates the loading rate has little effect on the crack length; that as loading rate is increased, the crack growth rate is decreased as the fluid pressure within the crack falls; and that at high loading rates the growth rate is lowered. Increasing fracture toughness, decreasing far-field pore pressure, and decreasing permeability have similar effects to those of increasing loading rate. For materials with very low permeability, such as shales, the loading rates at which such effects occur are within the range of laboratory experiments; suppression of tensile cracking and its replacement by shear cracking do appear to be seen. ¿ American Geophysical Union 1993