How do I use the read-only clause in a select statement

I´m using progress 9.1b Database.

How can I set the Select statement for read-only. I´m trying to make a select with the read-only clause and the sql explorer tool send me the "syntax error" message. In other DB the read only is the following:

SELECT * FROM xxx FOR READ ONLY, but it seems that progress can´t understand it... Thanks in advance..