OEL is not supported on cr1.8xlarge. These instances run as HVM-base instances. All Oracle AMIs are PVM. For HVM you have to go with Windows, SUSE or RHEL for now. You can spin one of these up and install Oracle DB on them. There are ways to convert a PV AMI to HVM AMI, but whether Oracle will support you is another question. This applies to the other cluster compute instances types as well: CC2 and CG1. However, it is mostly likely someone wants to run the cr1 instance type as this is the largest memory footprint by far (244 GB). This size instance is great for in memory databases or large EBusiness Suite/Fustion installations.