both shocks use oil as the damping fluid the only difference is that on the gas shock absorber there is a plunger with oil on one side & gas on the other ,the gas puts a constant pressure on the oil so the oil do not get aerated ( it stops the oil from going frothy )as aerated oil is crap as a damping fluid .so gas shocks are better when you are pushing your car hard keeping your shock absorbers working correctly for longer .hope that makes sense