Although solid deflagrants such as nitrocellulose, the most commonly used propellant in firearms, could be thought of as monopropellants, the term is usually reserved for liquids in engineering literature.
For the most part, researchers came to the conclusion that any single substance that contained enough energy to compete with bipropellants would be too unstable to handle safely under practical conditions.
[citation needed] The related "dinitrodiglycol", more properly termed diethylene glycol dinitrate in modern notation, was widely used in World War 2 Germany, both alone as a liquid monopropellant and colloidal with nitrocellulose as a solid propellant.
The polynitrates of long chain and aromatic hydrocarbons are invariably room temperature solids, but many are soluble in simple alcohols or ethers in high proportion, and may be useful in this state.
[citation needed] Hydrazine,[6][11] ethylene oxide,[12] hydrogen peroxide (especially in its German World War II form as T-Stoff),[13] and nitromethane[14] are common rocket monopropellants.
[17] Nitrous oxide generates oxygen upon decomposition, and it is possible to blend it with fuels to form a monopropellant mixture with a specific impulse up to 325 s, comparable to hypergolic bipropellants.