A technique for time-resolved, high-resolution distributed pressure sensing utilizing nonlinearly induced birefringence and polarization coupling in optical fibers is proposed. A theory of cross-interaction between two counterpropagating waves which agrees well with numerical simulations is presented. By measuring the relative power of the two principal polarizations of a probe wave at the fiber output, distribution of the linear birefringence along the fiber can be calculated, providing a convenient fiber optic sensor. The proposed sensor uses ultrashort pulses from mode-locked lasers and thus inherently possesses high spatial resolution and simplicity of the sensing head, in addition to the general features shared by all fiber sensors. >