Final answer:
The fuel type with mass and volume but no definite shape is a liquid. It assumes the shape of its container while retaining a consistent volume.
Step-by-step explanation:
The type of fuel you are asking about is liquid. Liquids have a fixed volume but do not have a definite shape. Instead, liquids take on the shape of their containers. This is one of the key characteristics that distinguishes liquids from solids, which have both a definite shape and volume, and gases, which have neither a definite shape nor a fixed volume and thus fully expand to fill their container. When considering the states of matter for a substance like fuel which is fluid and conforms to the shape of its container but maintains a constant volume, it is identified as a liquid state.