SELECT Substr(df.tablespace_name, 1, 20) "Tablespace Name",
       Substr(df.file_name, 1, 80) "File Name",
       Round(df.bytes / 1024 / 1024, 0) "Size (M)",
       decode(e.used_bytes, NULL, 0, Round(e.used_bytes/1024/1024, 0)) "Used (M)",
       decode(f.free_bytes, NULL, 0, Round(f.free_bytes/1024/1024, 0)) "Free (M)",
       decode(e.used_bytes,
              NULL,
              0,
              Round((e.used_bytes / df.bytes) * 100, 0)) "% Used"
  FROM dba_data_files df,
       (SELECT file_id, sum(bytes) used_bytes
          FROM dba_extents
         GROUP by file_id) E,
       (SELECT Max(bytes) free_bytes, file_id
          FROM dba_free_space
         GROUP BY file_id) f
WHERE e.file_id(+) = df.file_id
   AND df.file_id = f.file_id(+)
ORDER BY df.tablespace_name, df.file_name;