Integrated analysis of 4D seismic data and petrophysical data is used to produce probabilistic fluid and lithology volumes for monitoring reservoir performance on the Nelson Field. Petrophysical analysis of log data shows distinct fields for oil sand, water sand, shale and heterolithic‘ lithologies’ in acoustic impedance – Poisson's ratio space. Elastic inversion techniques applied to conventional 4D AVO datasets convert the reflectivity data to acoustic impedance, shear impedance, Poisson's ratio and angle impedances. The elastic inversion datasets are used to quantify oil–water contact movements through volume sculpting techniques. Well-derived relationships are used to predict 3D volumes of oil sand probability from three different seismic survey vintages: 1990, 1997 and 2000. Changes in oil sand probability due to production are verified by comparison with repeat production logs. Integrated volume interpretation of 4D far offset inversion difference (oil–water contact (OWC) movement) and oil sand probability shows areas of unswept oil, highlighting infill opportunities. Early results from infill drilling have validated the method, realizing the potential economic benefits of 4D seismic technologies.