SQL> select max(col1) col1
  2       , max(col2) col2
  3       , max(col3) col3
  4       , max(col4) col4
  5       , max(col5) col5
  6       , max(col6) col6
  7       , max(col7) col7
  8       , max(col8) col8
  9       , max(col9) col9
 10       , max(col10) col10
 11   from test;

      COL1       COL2       COL3       COL4       COL5       COL6       COL7
---------- ---------- ---------- ---------- ---------- ---------- ----------
      COL8       COL9      COL10
---------- ---------- ----------
        20        240          4          9        100         29         53
        66          4         86

SQL> SELECT max(n) n
  2    from ( select max(col1) n
  3             from test
  4            union
  5           select max(col2) n
  6             from test
  7            union
  8           select max(col3) n
  9             from test
 10            union
 11           select max(col4) n
 12             from test
 13            union
 14           select max(col5) n
 15             from test
 16            union
 17           select max(col6) n
 18             from test
 19            union
 20           select max(col7) n
 21             from test
 22            union
 23           select max(col8) n
 24             from test
 25            union
 26           select max(col9) n
 27             from test
 28            union
 29           select max(col10) n
 30             from test
 31*        ) x
SQL> /

         N
----------
       240

SQL> select greatest(max(col1)
  2                 ,max(col2)
  3                 ,max(col3)
  4                 ,max(col4)
  5                 ,max(col5)
  6                 ,max(col6)
  7                 ,max(col7)
  8                 ,max(col8)
  9                 ,max(col9)
 10                 ,max(col10)
 11                 ) ok
 12*   From test
SQL> /

        OK
----------
       240

SQL>

SQL> SELECT col_01
  2  ,      col_02
  3  ,      col_03
  4  ,      col_04
  5  ,      col_05
  6  ,      col_06
  7  ,      col_07
  8  ,      col_08
  9  ,      col_09
 10  ,      col_10
 11  FROM   t
 12  /
  
    COL_01     COL_02     COL_03     COL_04     COL_05     COL_06     COL_07     COL_08     COL_09     COL_10
---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ----------
        57         72         80         66         94          3         39         11         79         64
        87         93         40         23         37         86         96         50         53         12
        95         47         99         33         24         88         22          6         60         76
         8          2         46         75         78         49         62          0         21         36
        30         56         98         73         44         17         77         16         67         69
        42         41         54         55         97         90         31         91         61          5
        65         59         71          1         13         29          4         15         89         82
        92         25         70         32         68         26         14          7         38         34
        74         84         20         10         51         27         48         43         83          9
        18         85         58         45         52         19         81         28         35         63
  
10 rows selected.
  
SQL> SELECT MAX(GREATEST(col_01
  2             ,        col_02
  3             ,        col_03
  4             ,        col_04
  5             ,        col_05
  6             ,        col_06
  7             ,        col_07
  8             ,        col_08
  9             ,        col_09
 10             ,        col_10))
 11  FROM   t           
 12  /
  
MAX(GREATEST(COL_01,COL_02,COL_03,COL_04,COL_05,COL_06,COL_07,COL_08,COL_09,COL_10))
------------------------------------------------------------------------------------
                                                                                  <font color=red>99</font>
  
SQL>