I wish to make an animation of pouring water over oil or vice versa. In physical simulation, how do I make oil thicker than water and make both liquids behave realistically when stirred and left to settle?
The fluid simulation engine that ships with Blender isn't capable of mixing two fluids.
They would require two separate domains, with different parameters, being baked at the same time and reading the other domain's status frame-by-frame as input for themselves. Unfortunately, this kind of "simultaneous bake" isn't possible.