You can use the dbms_space package to find out the fragmented data blocks. The space__usage procedure is quite helpful in getting the information on free space in each block in a segment. There are fsl_blocks, fs2_blocks, fs3_blocks, and fs4_blocks parameters, which give information about blocks that have 0- 25, 25-50, 50-75 and 75-100 percent free space, respectively.