Load balance is important because it may affect the speedup attained through the concurrent execution of loop iterations on a parallel processor. We study loop load balance in the context of the well-known Perfect benchmarks. Several static and dynamic characteristics of the Perfect benchmark DOALL loops are observed and interpreted. Thelate arrival of processors is noted as a major source of load imbalance. This observation suggested the idea ofprocessor preallocation. An analytic cost model is presented and the advantages of processor preallocation are demonstrated by experimental evaluation on a CRAY Y-MP8 under the Unicos operating system.