The minimum-energy structure, vibrational frequencies, and thermodynamic properties of carbonyl diazide, OC(N3)2, have been determined using Gaussian-X compound methods. At ∼75% nitrogen by mass, carbonyl diazide can be considered a “green” high energy material because of the low amount of carbon-containing decomposition products it makes. Our calculations indicate that carbonyl diazide has a significantly high enthalpy of formation, but its specific enthalpy of decomposition is commensurate with current high energy materials.