Energies of atomic orbitals on molecular orbital diagrams When we plot molecular orbital diagrams we use a linear combination of atomic orbitals. 

Where can I find the energies of particular atomic orbitals?

In the picture below, the energies of 2s and 2p orbitals of Oxygen are lower than Carbon's 2s and 2p orbitals of Carbon, what is the logic behind this?
Ben Norris's comment is correct.  

An estimate of the atomic energies for orbitals may be gleaned from ionization energies, for example here:

http://periodictable.com/Properties/A/IonizationEnergies.html

Otherwise, the energies need to be calculated quantum mechanically.