A shipper who utilizes exclusively the vessels of the member lines of the conference for carriage of cargoes between the ports covered by the conference, will receive a rebate of a certain percentage (usually 10%) of his freight payments.The rebate is computed for a designated period (shipment period) usually three to six months but is paid after a period (deferred) period) of the same length following the shipment period, on the condition that the shipper has given his exclusive support to the conference lines, both during the shipment period, and the deferred period.