Question

Why is oil miscible in gasoline and immiscible in water?

Answer 1

Like dissolves in like only. This statement clearly states that the polar compounds dissolve in polar solvents, one of the examples for a polar solvent is water and non-polar compounds dissolve in non-polar solvents only, one of the examples for non-polar solvents is gasoline or kerosene.

Complete answer:
Hydrocarbons are compounds consisting of only carbon and hydrogen atoms. Examples of hydrocarbons are alkanes, alkenes, and alkynes. Alkanes are the unsaturated hydrocarbons, whereas alkenes and alkynes are the unsaturated hydrocarbons.
Gasoline has the chemical composition of $4 - 8\%$ alkanes, $2 - 5\%$ alkenes, $25 - 40\%$ isoalkanes, $3 - 7\%$ cycloalkanes, $1 - 4\%$ cycloalkenes, and $20 - 50\%$ aromatics. The aromatics mostly consist of benzene.
Hydrocarbons are nonpolar due to the absence of polarity or movement of electrons. As gasoline consists of hydrocarbons, it can be considered non-polar.
Oil is nothing but a mixture of hydrocarbons. Thus, oil is also a non-polar compound.
As polar compounds dissolve in only polar solvents. Oil and gasoline become miscible which means they completely dissolve in one another and form a homogeneous solution.
Whereas water is a polar compound. Thus, oil and water when mixed become immiscible which means they can be seen as separate layers.

Note:
Gasoline can be used as the main fuel in engine vehicles. It can be produced in petroleum refineries and blending machinery. Due to the presence of different hydrocarbons, it can be considered a non-polar compound. The miscibility of solutions can be decided by their nature and extent of solubility.