How does the oil from liver provide a limited buoyancy in absence of swim bladder?

Oil from the liver does not provide buoyancy in the absence of a swim bladder.

Fishes which lack a swim bladder, have bodies denser than water and will sink if they do not engage in constant swimming. Some bottom-dwelling fishes, such as sculpins and flounders, use this lack of buoyancy advantageously, enabling them to rest on the sea floor without any effort.