Hi I had faced an interesting scenario yesterday when I moved some code from Dev to QA and tried to execute the queries, they behaved very differently. QA was newly refreshed with the data using Export/Import. I had clalcuated the Stat using 9i DBMS_STATS and auto sample size. I had even copied the Stats from dev to QA to make sure that stats are same but it still failed. The only difference between Dev and QA is that QA might have few more record than Dev as Dev was refreshed from Prod one week BAck. Anyway Data will continue to change in Production and so I don't think that one week Data change shoudl be an issue. There is no Hints been used and all init.ora setting including sga size are same. I had a script of around 15-20 query and each query is very big about 5-20 pages. Half of them are working fine while others are hanging. Trace will also show that it is running but I appreciate if you can provide any insight as what else can be done, Explain Plan is more or less the same except that their sequence are different and I don't understand as why it happen when even Stats are new or even copied using dbms_stats.export.. procedure. TIA Sanjay --------------------------------- Everyone is raving about the all-new Yahoo! Mail beta.