An inversion methodology and algorithm is developed for inverting Magnetotelluric data for threedimensional Earth conductivity models meshed using unstructured grids. The forward modeling subset of the inversion method is implemented using the E-field vectorial finite-element method for layered or homogeneous Earth models and complex target geometries. The inversion is based on the iterative linearized Gauss-Newton approach with the Jacobian matrix-vector operations calculated implicitly for the sake of memory and storage efficiency. The algorithm is parallelized for multiple frequencies and demonstrated to be feasible in terms of computation time and model accuracy. Preliminary results due to a successful implementation of the algoritm is shown for the Commei 3D-2A model.


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