Liquid rocket fuels are propellants used in rocket engines that exist in a liquid state. These fuels typically consist of a fuel, such as liquid hydrogen or kerosene, and an oxidizer, like liquid oxygen. When combined and ignited, they produce a high-temperature gas that expands rapidly, generating thrust to propel the rocket. The use of liquid fuels allows for precise control over the engine's thrust and burn time, making them suitable for various missions, including launching satellites and crewed spaceflights. Notable examples of rockets using liquid fuels include the Space Shuttle and the Falcon 9.