Empty Weight (EW)
Empty weight includes the airframe, engine and fixed equipment as necessary for flight. Empty weight also includes unusable fuel and undrainable oil. Empty weight does not include pilot and payload, and ballast or usable fuel.
Basic Empty Weight (BEW)
Basic empty weight includes the airframe, engine, fixed equipment, unusable fuel, full oil and other items necessary for all flights. The basic empty weight does not include pilot, payload (passengers and freigh), or ballast (for balance) or usable fuel. The basic empty weight (and moment arm) will be different for each individual aeroplane, and is always specified in that particular aeroplane's flight manual.
Reference: Robson, David. "Chapter 10: Loading." Basic Aeronautical Knowledge (BAK). Darra: Aviation Theory Centre Pty, 2009. 317. Print.
Basic empty weight includes an extra item over empty weight which is full oil.
What is Full Oil?
Hope someone can explain this. Thanks!