Because shipping is a service business, ship demand depends on several factors including price, speed, reliability and security. It starts from the volume of trade and we discussed how the commodity trades can be analysed by dividing them into group which shared economic characteristics such as energy, agricultural trades, metal industry trades, forest products and other industrial manufactures. However to explain how transport is organized we introduced the parcel size distribution. The shape of the PSD function varies from one commodity to another. The key distinction is between ‘bulk cargoes’, which enters the market in ship size consignments and ‘general cargo’, which consists of many small quantities of cargo have to be grouped for shipment.