The main source of plasma in the Jovian magnetosphere is Io and the dominant sink is outward radial transport. Conservation of angular momentum leads to a decrease in angular velocity with distance, but ionospheric coupling resists any departure from corotation. Competition between these effects predicts a radial dependence for the lag that agrees with observations out to some moderate distance in the middle magnetosphere. However, the observed angular velocity farther out appears to saturate at roughly half the planetary angular frequency, in contrast to the theoretical prediction that it continue to decrease asymptotically to zero. This paper reviews the theory of this phenomenon and explores three of its underlying assumptions as candidates for explaining this discrepancy: (1) Field line stretching from the assumed dipole configuration; (2) a variation in the ratio of the average angular velocity to the average weighted by mass outflux; and (3) a nonlinear response in the atmospheric component of the system.¿ 1997 American Geophysical Union