First I would not use rf to measure level of petrol, require a very very fast clock and counter detecting rf phase. I would use either a differantial pressure transducer, ultrasonic level detector (preferred), or some other kind of level detector.
The transducer would be read by a microcontroller, PLC, or some kind of DAQ which would use rf to transmit the level and/or control the valves and pumps to maintain the level.
If you want to control level from the far side use tranceivers and send the commands back to the level monitor/pump valve controllers to set petrol level.
The rf part depends on the distance between transceivers. If it is less than 1KM line of sight then you could use something like 2.4GHz Xbee pro, these are digital no encoder or decoder required. For longer distances use 900MHz Xbees or GSM.