  The global existence of weak solutions to the three space dimensional Prandtl
equations is studied under some constraint on its structure. This is a
continuation of our recent study on the local existence of classical solutions
with the same structure condition. It reveals the sufficiency of the
monotonicity condition on one component of the tangential velocity field and
the favorable condition on pressure in the same direction that leads to global
existence of weak solutions. This generalizes the result obtained by Xin-Zhang
on the two-dimensional Prandtl equations to the three-dimensional setting.
