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In this talk we introduce the Wave Equation Based AVO Inversion (WEB-AVO) method as a means to tackle the thorny issue of residual gas (also known as “fizz-gas”) characterization using pre-stack seismic data. WEB-AVO inversion is a unique approach, not only because it includes interbed multiples, mode conversions and transmission effects into the scheme, but also because it derives compressibility from seismic data directly. Compressibility is the reciprocal of bulk modulus, and it proves to be very sensitive to saturation changes within the reservoir, documented in earlier work, see Gisolf, 2016 . Historically, workflows like Near vs Far amplitudes or linear inversions have failed to address the issue mainly due to the relative lack of sensitivity to saturation, coupled with the presence of multiple scattering in the area that tends to take its toll on the far offsets. While Contreras et al, 2020 , have indicated the power of this workflow to predict residual gas accumulations, we will hereby analyze the workflow and support the claim in a case study from the NW Shelf of Australia.