A parallel nonlinear solver (Paloschi, 1994) is implemented in the flowsheeting package SPEEDUP(Aspen Technology Inc.). The solver is a Quasi-Newton (QN) method approach where the parallelization is achieved by partitioning the domain and range of the system of nonlinear equations, assigning one partition to each available processor. All significant tasks within the QN algorithm are performed in parallel. Linear systems are solved using a parallel preconditioned iterative linear solver (GMRES) and the preconditioner is based on a block-diagonal approximation. It is tested by using two steady-state simulation problems. The first is a plug-flow reactor flowsheet involving 1633 variables in the largest nonlinear block. The second example consists of a flowsheet with two columns, resulting in a problem with 5668 equations in the largest nonlinear block. Two MIMD parallel machines are considered. The first is a cluster of workstations running with the message passing protocol PVM. The other is a proper parallel machine, a FUJITSU AP1000. The larger problem is tested in both machines to compare the parallel performance. For the first example, the execution time is reduced by a factor of 2.4 using 8 processors and 1.5 using 4 on the Fujitsu AP1000 machine. For the second example, the reduction achieves a factor of 2.7 using 8 processors on a cluster of workstations and a factor of 7.1 using 16 processors on the Fujitsu AP1000. (C) 1998 Elsevier Science Ltd. All rights reserved.