To answer julian's question: Each rbs currently has 3 min extents and max extents unlimited.

The dba keeps changing the rbs's. Current settings are:
7 rbs, 3 min extents, 30 meg initial & next, Optimal 90 meg.

Tell your DBA that a guy over the Intenet :-) told you to modify a bit the RBSs in the following way: 20 min extents, initial and next 1M, optimal 20M, and the number of rollback segments should equal (for 8i for example) number of concurrent users/4. Usually 4-8 RBSs is OK.