How do cephalopods regulate their buoyancy?

There are many ways a cephalopod maintains buoyancy, depending on the species.  Nautlioids allow gas to take over the space between their shell and their body.  Some cephalopods allow fresher water to come from their kidneys and force the salt water out of their bodies so that they can be less dense than the surrounding water.  Some octopuses are very gelatinous and have chlorine ions in place of sulfate, which makes them lighter.  Still others accumulate oils in the liver.