How do I identify all super users in SQL Server?
You can use this code:

SELECT   name,type_desc,is_disabled, 
         (IS_SRVROLEMEMBER ('sysadmin',name)) AS ISSRVROLE
FROM     master.sys.server_principals 
-- WHERE    IS_SRVROLEMEMBER ('sysadmin',name) = 1
ORDER BY name ;


sys.server_principals - Contains a row for every server-level principal

IS_SRVROLEMEMBER - Indicates whether a SQL Server login is a member of the specified server role.

You would also need to check for the sysadmin-equivalent CONTROL SERVER permission for the server principal in sys.server_permissions.

IS_SRVROLEMEMBER can return:


0 -  login is not a member of role.
1 - login is a member of role.
NULL - role or login is not valid, or you do not have permission to view the role membership.