The widely investigated organic substance o-terphenyl (OTP) displays thermal and kinetic behavior prototypical for "fragile" glass formers. The special relationship between its heat capacity in supercooled liquid, amorphous glass, and crystalline solid states provides simple access to the enumerating distribution function for its amorphous inherent structures (potential energy minima) by depth. The thermodynamic calculations required at 1 atm yield a broad and somewhat asymmetric distribution. This distribution implies that supercooling OTP from its melting point (329.35 K) to its glass transition (240 K) succeeds only in reducing inherent structure enthalpy by 66% of the amount that would be required to attain the most stable amorphous inherent structure.