I have centos 6.4 64. In /boot/efi/EFI/redhat I have grub.efi file (about 251Kb). However, when I execute efibootmgr I getFatal: Couldn't open either sysfs or procfs directories for accessing  EFI variables. Try 'modprobe efivars' as root.My question what do I use - BIOS or UEFI?
Centos 6.4 and UEFI
linux;centos;uefi;bios
This page suggests you need BIOS or a more recent version of CentOS 6: http://wiki.centos.org/HowTos/UEFI.