A method for spatially interpolating pressure values of seismic data uses known values of pressure and spatial derivatives of pressure at a plurality of irregularly spaced locations along the direction of interpolation. The interpolation preferably uses an interpolation operator calculated by assuming that an interpolated pressure value comprises a linear combination of the known pressure values at locations xi and the spatial derivatives at locations Xα, with operator coefficients wi and wα respectively, and calculating the coefficients by minimizing an error function.