To my knowledge, memory in system administration terms is allocated, not indexed. So I suppose you mean how much RAM Oracle Linux 6.3 x86 can possibly allocate. See here:
... which shows 64 GB for x86 32-bit Oracle UEK kernel. However as far as I'm aware you need a i686 CPU, meaning Pentium II or later.
Btw, the product is no longer called Oracle Enterprise Linux. It's Oracle Linux, or OL. There is usually no valid reason to limit your OS to 32-bit processing or to install Oracle 32-bit software on any modern hardware.
Note that regardless of how much total memory the OS can see using a x86 kernel, processes are still limited by 32-bit addressing and cannot use more than about 3 GB of memory.
Edited by: Dude on Mar 7, 2013 1:31 AM
The max amount supported by the original RHEL kernel is apparently 16 GB.