you should be able to open the oil cap and look at the dipstick to see if there is any residual oil on it to see what color it is--it's not always easy to see from the outside of the tank. If the tank is actually bone dry, then after you add the proper oil, you will need to bleed the system to make sure engine is not running without any oil. Or...it's possible that whoever owned it before you has converted it to a premix...which means you MUST mix gas and oil together, and the tank doesn't really have oil in it.