Water sat in the middle, and oil rose to the top. As a bonus, we decided to drop some solids into our solution. After making hypotheses, we found the penny to lie on the bottom of all the liquids, a lego brick to sit on top of the water, and a wood chip to float on top of the oil. The liquids are all more dense than the wood chip. To learn more about solids, liquids and their densities, we experimented with an egg in a large glass of fresh water.
Salt dissolved in water increases the density of water.
Denser liquids are better at keeping objects afloat. This is why many things that sink in fresh water will float in salt water.