In the presence of an emulsifying agent, a mixture of oil and water becomes a

Colloidal dispersion or emulsion

Explanation:

The colloid of a liquid in liquid (both dispersed phase and dispersion medium are liquids) is known as emulsion or colloidal dispersion.

We know that oil and water are immiscible liquids. In order to make them miscible we have have add emulsifying agents.

An emulsifying agent has a long non polar hydrocarbon chain (in general) and a polar head.

For example salts of fatty acids.

The polar head is hydrophilic and non polar tail is hydrophobic.

It causes the miscibility of the two polar and non polar liquids