This paper proceeds as follows. First, I review the essential theory underlying the angle-dependent reflectivity estimation, and the subsequent impedance inversion. Next, I show an application of the theory and algorithms to a marine data set acquired in the Gulf of Mexico over a known producing gas reservoir. This real data pilot study includes a high-resolution migration velocity analysis, a prestack angle-dependent reflectivity estimation, and a subsequent linearized Zoeppritz inversion for relative contrasts in P and S impedance. Finally, I calculate a single hydrocarbon indicator map which correlates well with the known gas interval, and suggests lateral variations in gas saturation. The results of this study seem to validate the theory and algorithms I use here.