Yes, generally they are complex quereies involving both inner and outer joins. SQL 2000 would join the Inner Join tables first since they were the most likely to reduce the result set. SQL 2005 does not necessarily join the tables in that order since sometimes the outer joined tables may be very small. But sometimes when the optimizer chooses to perform the outer join first, the result can be a cartesian product. You will see a No Join Predicate warning in the execution plan and high CPU utilization with LOTS of reads. There is a known bug (#50001820) that is similar to this that was fixed in SP 2, CU 4 but it does not address all occurances of this problem. Adding a Force Order hint on SQL 2005 results in a better execution plan for these queries.