If you had exhausted of space, and tried to find a quick way of resizing the tablespaces. You may want to use TOAD feature: From Administer ->Tablespaces-> Select one tablespace and press F4. In the opened window click datafiles tab and double click the datafile which you want to resize. In this window there is a button “Minimum Size?”, click it. After some time of processing, it will find the minimum size of datafile it could be, it could be better than trial-error method for exact sizes.