The empirical trend of the empty weight ratio of long range subsonic jet transports is analysed in order to enable the cruise performance of very large aircraft to be predicted. Each of the main items which go to make up the empty weight is dealt with individually in order that the effect of size on each can be established. Consideration is given to the effect of increased wing loading on take off runway requirements. It is concluded that it would be feasible to produce an aircraft capable of carrying up to 1000 passengers over the great majority of all transatlantic routes. Such an aircraft would have an empty weight ratio of about 0.5 and would weigh approximately twice as much as the largest subsonic jet at present in existence.