1. A method of determining the existence of and location of hydrocarbon and water fluid contacts by analyzing spatial changes in 3D seismic data comprising the steps of: a. obtaining 3D dip data and azimuth data as at least one set of 3D volume data and deriving corresponding 3D reliability volumes or deriving 3D censor volumes which are representative of portions of the at least one set of 3D volume data within which 3D dip data and azimuth data can be reliably computed; b. selecting a focused subvolume of interest within the at least one set of 3D volume data; c. determining reliability locations within the focused subvolume of interest having non-null 3D dip data and non-null 3D azimuth data within the 3D reliability volumes or 3D censor volumes across the focused subvolume of interest forming a sequence of reliability locations; d. computing an average for a plurality of vector dips around each reliability location in the sequence of the reliability locations forming at least one structural dip vector for each reliability location; e. identifying a local subvolume of interest interior to the focused subvolume of interest for each reliability location wherein the local subvolume of interest contains 3D dip data and azimuth data as a set of vectors; f. determining a flat spot direction vector for each structural dip vector at each reliability location; g. forming a set of candidate flat spot dip vectors from at least one vector in the set of vectors within the local subvolume of interest and the at least one vector in the set of vectors are statistically consistent with the flat spot direction vector; h. computing a significance measure for each vector within the set of candidate flat spot dip vectors; i. forming and storing a 3D output subvolume comprising significance measures for all vectors in the set of candidate flat spot dip vectors; j. repeating the method for all 3D volume data forming a 3D output volume.