Algorithms which utilize multiprocessing computers are considered for
the numerical solution of variational inequalities. Parallel versions
of the SOR algorithm with projection to the constraint set are careful
ly studied. One, analysis assumes the matrix is a symmetric M-matrix a
nd uses multisplitting and upper solutions to deduce convergence of th
e parallel algorithm. Another analysis uses the constrained minimizati
on characterization of variational inequalities and P-regular multispl
ittings to obtain convergence. Numerical experiments were done on vect
or/multiprocessing computers. When using properly ordered multisplitti
ng versions of SOR with projection to the constraint set, substantial
speedups of the vector/multiprocessing codes relative to the serial co
de are observed. Applications to fluid flow in a porous media and to a
control problem are examined.