(1) No, all objects that sink in water, don’t sink in oil.
(2) Oil is less dense than water as it floats on the surface of anybody of water.
(3) Due to the differences in the density of water and oil, some objects which sink in water may float in oil.
(4) Some objects which sink in water they too sink in oil also.
(5) This is all depending up on the densities of water, oil and substance what we are taking to test.