manage User Rol and Object Privilege question - grant 'select tables' to a Role, then grant role to

Hello friends:

Here is a basic question could be simple as I used to think about it - but it didn't work as expected - user cannot see table data (select doesn't work).  Oracle version is 10.2.0.1.  Application is Siebel crm.

we frequently got developers' request that users need to 'select-only' priviledge to access some tables.  Thus, we design it by creating a Role, and then granting 'select privilege' to tables to Role, and then grant the role to user.  The steps are in below:

(1).  Create role RO (for 'read-only'):

 Select 'GRANT SELECT ON OwningUser.'||Table_Name||' TO RO;'