This paper presents the results of experiments and simulations conducted to investigate the effect of mobile oil saturation on the fracturing fluid leakoff characteristics under dynamic conditions in high permeability reservoir rocks. The fluid leakoff behaviour is examined for samples of varying permeability. In addition, the effectiveness of fluid loss additive in the presence of mobile oil saturation is investigated. A conceptually consistent model to predict the leakoff rate in the presence of mobile oil saturation at the fracture face has been developed. The model is validated using data obtained from dynamic leakoff tests. The results demonstrate that the presenece of mobile oil saturation at the fracture face causes the leakoff characteristics to be very different from the tests for which the fracture face is completely saturated with brine. The leakoff characteristics are also affected by the fracture face permeability.