Liquids and solids sure, but for gases are you referring to the level concentration of specific gasses? Also, the accuracy will depend on the environment you are placing the sensor in, high temperature, or pressure. Check out ultrasonic sensors for level detection. There is also a company that is using microwave technology in the same fashion as ultrasonic sensors. For a higher level of accuracy, I would think a float level sensor would work, but you will need to look around for a supplier that can meet your accuracy requirements.
Liquids and solids can be measured by Time of Flight sensors like radars, ultrasonic, GWR or laser systems. Usually there are different models for liquids and solids, with different algorythms to interpretate the reflected echoes that differ a lot between the two conditions. Electromechanical Bob level sensors could do it but with different weight designs, I wonder what means measuring the level of a gas... maybe the density or the level of liquified gasses LPG, LNG? The only systems that can measure at the same time level and gas density are radiometrics
