In analyzing neutrino oscillation experiments it is often assumed that while new physics contributes to neutrino masses, neutrino interactions are given by the Standard Model. We develop a formalism to study new physics effects in neutrino interactions using oscillation experiments. We argue that the notion of branching ratio is not appropriate in this case. We show that a neutrino appearance experiment with sensitivity to oscillation probability P i j e x p can detect new physics in neutrino interactions if its strength G N satisfies (G N G F ) 2 P i j e x p . Using our formalism we show how current experiments on neutrino oscillation give bounds on the new interactions in various new physics scenarios.