A liquid mixture of complex hydrocarbon compounds is called crude oil.

Here's why:

* Hydrocarbons: The primary components of crude oil are hydrocarbons, which are organic compounds made up of hydrogen and carbon atoms.

* Complex: The hydrocarbons in crude oil are complex, meaning they have varying chain lengths, branching patterns, and sometimes even cyclic structures.

* Liquid: Crude oil exists as a viscous liquid at room temperature.

While there are other liquid mixtures of hydrocarbons, "crude oil" is the most common and specific term for this type of mixture.