A general scheme of two-level parallelization (TLP) has been described for direct simulation Monte Carlo of unsteady gas flows on shared memory multiprocessor supercomputers. The high efficient algorithm of parallel statistically independent runs is used on the first level. The data parallelization is employed for the second one. Two versions of TLP algorithm are elaborated with static and dynamic load balancing. The dynamic processor reallocation technique is used for the dynamic load balancing. Two gasdynamic unsteady problems were used to study speedup and efficiency of the algorithms. The conditions of the efficient usage of the algorithms have been determined.