From the late nineteenth century, shipping conferences became a pervasive feature at ports throughout Asia and other developing areas. Yet the effect which a conference system could have on the local mercantile structure in ports, where it was dominant, remains little explored. The present paper analyses how, in Singapore, overseas shipowners became monopoly sellers of shipping services through organising a conference system; the benefits which accrued to a powerful group of local merchants from supporting this system; and the Japanese response centred on the export of rubber. The first section below develops a model of the agreement between shipowners in Europe and the United States and their Singapore merchant counterparts, while the following two consider respectively the bargain struck and its impact on the local mercantile structure. Japanese merchants were relative late-comers to Singapore. They arrived in force only from the onset of World War I, after European merchants in the port and shipowners had already reached agreement between themselves. The penultimate section considers how, by the mid-1930s, Japanese merchants in Singapore and shipowners in Japan were able to mount an effective challenge to the European monopoly. The concluding section reflects on this challenge and suggests that it accords with the model of the advantages from business integration put forward in the section below.