Water molecules form hydrogen bonds with each other and exclude oil, as oil is a hydrophobic or non polar substance.
It is a polar molecule which has no taste, odor, or transparency, where  nucleus of the oxygen atom  of water attracts electrons strongly than the nuclei of the hydrogen atoms.
Water molecule  shows strong cohesive property where the attraction of molecules for other same kind of molecule is referred to as cohesion.
Water molecules composed up of one oxygen atom and two hydrogen atoms are hydrophobic or water fearing, oil is non polar molecule can not  attracted to water molecules, As a result oil and water can not mix.
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