Pressure transient data from a hydraulic fracturing experiment have been analyzed using a numerical model. Several system parameters and their sensitivities were evaluated, assuming a vertical, penny-shaped fracture geometry. Although the best-fit parameters may not constitute a unique set, they do appear credible from what a current field experience would indicate. It was found that the injection pressure transient is sensitive to initial fracture apeture, fracture stiffness, minimum horizontal stress, rock toughness, and host-rock permeability.