SQL> delete from t where x <= 6 -- totally clear blocks 1 and 2;
6 rows deleted.


SQL> delete from t where x = 7  -- remove 1 row from block 3;
1 row deleted.


SQL> analyze table t compute statistics;
Table analyzed.

SQL> select avg_space, blocks, empty_blocks, num_freelist_blocks
  2    from user_tables

  3   where table_name = 'T';

  AVG_SPACE    BLOCKS   EMPTY_BLOCKS   NUM_FREELIST_BLOCKS
  ---------    ------   ------------   -------------------
       2643        35             28                     4