When installing Oracle Enterprise Linux in VirtualBox, or downloading one of the available images on Oracle Developer Days, it can be tricky installing the Guest Additions. I was struggling with those, until I found a very useful blogpost by R.Wang. This worked like a charm for me!
Only thing you might want to check, is the kernel version you are using. In bullet 5 is referred to the KERNEL_DIR. In your specific case the version number might be different. go to /usr/src/kernels and check for the latest kernel version in that directory. Also, there was no need for me to alter the yum.repos.d.
You can find the steps for installing the Guest Additions right here.
