This implies a high combustion temperature and exhaust gases with small molecular weights. Using low density propellants means that larger storage tanks will be required, thus increasing the mass of the launch vehicle. Storage temperature is also important. A propellant with a low storage temperature, i.e. a cryogenic, will require thermal insulation, thus further increasing the mass of the launcher. The toxicity of the propellant is likewise important.
Safety hazards exist when handling, transporting, and storing highly toxic compounds.
Also, some propellants are very corrosive, however, materials that are resistant to certain propellants have been identified for use in rocket construction. Petroleum fuels are those refined from crude oil and are a mixture of complex hydrocarbons, i.e. organic compounds containing only carbon and hydrogen. It is used in combination with liquid oxygen as the oxidizer. It also powered the first-stages of the Saturn 1B and Saturn V rockets. RP-1 delivers a specific impulse considerably less than cryogenic fuels.