This is a simple SQL statement to get you a list of all users and their roles in the Oracle DB:

“SELECT * FROM DBA_role_privs;”

And if you want to get the list of users related to a specific role, you can simply modify the SQL statement to be like this:

“SELECT * FROM DBA_role_privs where GRANTED_ROLE=’SSE_ROLE’;”

Source: http://www.dbforums.com/oracle/1650816-how-get-list-all-users-their-roles.html