©　2011　SEG.　We　present　a　method　for　estimating　quality　factor　Q　from　pre-stack　CMP　records.　First　employing　a　function　with　four　undetermined　parameters　to　approximate　the　source　wavelet,　the　relation　between　the　instantaneous　frequency　(IF)　at　the　envelope　peaks　of　seismic　wavelets　(EPIF)　and　offsets　is　derived　based　on　the　theory　of　one-way　wave　propagation　in　a　1D　viscoelastic　medium;　then　we　calculate　the　EPIF　of　every　non-zero　offset　trace　of　every　event　to　extrapolate　the　EPIF　of　zero　offset　trace　of　every　event　based　on　the　relation;　finally　Q　is　estimated　by　combining　WEPIF　with　the　reflectivities　information.　Applied　to　prestack　CMP　models　and　field　record,　it　produces　a　Q-curve　which　indicates　that　the　extent　of　absorption　corresponds　well　to　the　gas　saturation　of　reservoirs.