Two SD seismic data sets from the Lena field, U,S, Gulf of Mexico were analyzed for time-lapse effects. The time-lapse differences for the B80 reservoir are compared with production data, geologic models, flow simulations, and forward seismic models. A time-lapse-seismic-difference anomaly represents a region of gas invasion, and areas bypassed by the injected gas have been identified for infill drilling.