The polarization of Xe-129 gas by spin exchange with optically pumped Rb vapor is investigated in high magnetic field. Operation in a high field provides added spectral dispersion via Zeeman shifts of the electronic transitions. This simplifies the physics of the pumping process in such a way as to make it more amenable to treatment with simple rate theory. A relationship between the steady state Xe-129 polarization and the applied laser power is derived which agrees with experimental. results. This theory serves as a guide to the manufacture of very high polarizations of Xe-129 gas.