3D AVO (Amplitude Variation with Offset) analysis has evolved as an important interpretation method of 3D seismic data, in the last decade. A new approach is proposed in the present work for quantitative AVO analysis of 3D seismic data. The method is based on fitting the observed seismic data, in a least-squares approach, to a function of average angle (average of angle of incidence and angle of transmittance) or offset. The aim of the method is to obtain the estimates of changes in the elastic parameters (P-wave modulus, S-wave modulus and density) at a particular output location, using a combination of pre-stack Kirchhoff migration and matrix inversion. The method includes ways to do migration velocity analysis and estimation of dip. As a further extension, the method is modified to find out the orientation of vertical fractures and the extent of anisotropy, for the case when an isotropic medium overlies a vertically fractured medium.