The effect of a general oblique magnetic field on the development of Rayleigh–Taylor instability has been investigated. It has been demonstrated that n2 is purely real, where n is the growth rate of disturbance. Also in this case, the solution is characterized by a variational principle. The exact solution for the case of two superposed fluids has been derived when the oblique magnetic field is constant. It is shown that when the lighter fluid is topped by the heavier fluid a mode of maximum instability exists if the ratio of horizontal to vertical magnetic field is sufficiently large. No normal mode solution is possible if the lighter fluid lies atop the heavier fluid. Use has been made of variational principle to obtain the approximate solution of a fluid having exponentially varying density. It is found that for some disturbances, the oblique magnetic field has a greater stabilizing influence compared to a horizontal or vertical magnetic field of the same strength.
