By default, Ubuntu 12.04 doesn't have a hibernate option and it can be re-enabled if the hardware supports hibernation. For that,
1. Create the file:
vi /etc/polkit-1/localauthority/50-local.d/com.ubuntu.desktop.pkla
2. Add the lines:
[Re-enable hibernate by default]
Identity=unix-user:*
Action=org.freedesktop.upower.hibernate
ResultActive=yes
3. Save the file, restart the machine and new menu item should appear under the system button in upper right corner
