| Parallel data ow analysis methods o er the promise of calculating detailed semantic information about a program at compile-time more e ciently than sequential techniques. Previous work on parallel elimination methods 1, 2] has been hampered by the lack of control over interval size; this can prohibit e ective parallel execution of these methods. To overcome this problem, we have designed the region analysis method, a new elimination method for data ow analysis. Region analysis emphasizes ow graph partitioning to enable better load balancing in a more e ective parallel algorithm. In this paper, we present the design of region analysis and the empirical results we have obtained that indicate (1) the prevalence of large intervals in ow graphs derived from real programs, and (2) the performance improvement of region analysis over parallel Allen-Cocke interval analysis. Our implementation analyzed programs from the Perfect Benchmarks 3] and netlib 4] running on a Sequent Symmetry S81.Index Terms | Data ow analysis, elimination algorithms, interval analysis, parallel algorithms, program optimization. 1 In 20], Reps proves hardness results for some interprocedural data ow problems, assuming the \meet-overall-valid-paths" precision, and uses them to assert the non-existence of fast (NC-class) parallel algorithms for these problems. Nevertheless, he also points out that for the imprecise version of interprocedural data ow analysis, there does exist a fast (NC-class) parallel algorithm. Moreover, the worst case time complexity of useful data ow techniques are not observed in practice. 2 The available expressions problem involves information necessary for common subexpression elimination 19].