how do you determine that we are using OEL not Red Hat Linux?

How do you determine that we are using OEL (Oracle Enterprise Linux ) not Red Hat Linux?

[root@db-prod u01]# uname -a
Linux db-prod.afitaihi.loc 2.6.39-400.209.1.el5uek #1 SMP Tue Sep 10 20:33:17 PDT 2013 x86_64 x86_64 x86_64 GNU/Linux

[root@db-prod u01]# cat /etc/redhat-release
Red Hat Enterprise Linux Server release 5.10 (Tikanga)

So I thought we are using 'Red Hat Enterprise Linux Server',
but the UNIX admin says it is actually OEL.

How do you tell it is OEL?

Solution:

This is a Oracle Enterprise Linux Server:

[root@db-prod u01]# rpm -qf /etc/redhat-release
enterprise-release-5-10.0.3

This is a Oracle Server:

[root@erptest ~]#  rpm -qf /etc/redhat-release
redhat-release-5Server-5.7.0.3

This is a Redhat Server.

If the output of 'rpm -qf' has "enterprise" in it, you are running OEL.