A method of processing seismic data is provided in the seismic data is acquired at a plurality of locations and the method comprises interpolating and/or extrapolating the seismic data, thereby to estimate seismic data at a target location different from the plurality of locations. The interpolating and/or extrapolating the seismic data is performed in a polar co-ordinate system. The method may provide for, among other things, accuracy of estimation; particularly at short offsets from the seismic source. The polar co-ordinate system used may be chosen to approximate the seismic wavefront in an earth model, for example in an earth model in which properties vary only with depth.