Most rockets are fueled by liquid propellant, a mixture of liquid fuel and liquid oxidizer. These two substances are stored in the rocket, but in separate tanks. They are combined in a combustion chamber, where they are ignited and produce the energy that propels the vehicle. Typical liquid rocket fuels include alcohol, kerosene, hydrazine, and liquid hydrogen; typical liquid oxidizers include nitrogen tetroxide and liquid oxygen. Some rockets use solid rather than liquid propellant. In this case, the oxidizer and fuel are already combined in a dormant solid state. When the mixture is ignited, the entire amount of propellant is consumed in a single controlled combustion reaction. Solidfuel rockets are generally made to have more thrust than liquid-fuel rockets; also, they are lighter, simpler to design, and do not have nearly as many moving parts. Liquid-fuel rockets, on the other hand, can be turned on and off, and the amount of their thrust can be carefully controlled for performing delicate maneuvers.