Posco of South Korea, the world's fourth-largest steelmaker, has moved to strengthen the security of its coal supplies by joining ArcelorMittal and China's Citic on the share register of Macarthur Coal. The three groups together now control almost half of the A$4.2bn (US$4bn) Australian group, making it virtually impossible for one of them to launch a successful takeover bid for Macarthur without the others' agreement. The sharp escalation in coking coal prices has highlighted Macarthur's value. The group accounts for about a third of the export trade in pulverised coal, a highly efficient form of the mineral favoured by steelmakers. Posco said yesterday it had invested A$420m in a 10 per cent stake in Queensland-based Macarthur at A$20 a share - the same price paid by ArcelorMittal, the steelmaker headed by Lakshmi Mittal. In April, Posco was forced to accept a 205-210 per cent rise for its supplies of coking coal from Australian miners. The Korean steelmaker is still in negotiations with Rio Tinto and BHP Billiton on iron ore price increases, which are likely to be in the magnitude of the 96.5 per cent rise recently agreed by Chinese steelmakers. The South Korean group's investment follows ArcelorMittal's move at the weekend to increase its stake in Macarthur from 14.9 to 19.9 per cent, the maximum allowed in Australia before a full takeover must be launched. The deal came just days after the Luxembourg-based group, Macarthur's biggest customer, suspended talks with its board over a potential bid. Both Posco and ArcelorMittal acquired their holdings from Ken Talbot, Macarthur's founder, who resigned from the board last week in order to maximise the sale proceedings from his stake of almost 20 per cent. Analysts said the stalemate could be broken by Citic, the Chinese investment group, which has indicated it might be a seller of its 17.7 per cent stake. But they also said the three groups might be content to sit on their stakes in order to keep Macarthur independent. ArcelorMittal scooped up its initial 14.9 per cent stake in Macarthur in May, in a move that precipitated the failure of takeover talks with another suitor, widely believed to have been Xstrata, the Anglo-Swiss mining group. Copyright The Financial Times Limited 2008