German automaker BMW wants a stake in SGL Carbon, already one of its strategic partners and the leading carbon-based product maker, the weekly Der Spiegel reported Sunday. \"We have a fundamental interest in SGL Carbon,\" a senior BMW executive told the magazine. It was not clear how high a stake BMW might be taking, but if it had more than 20 percent it would effectively control the company. Billionaire Susanne Klatten, the heiress to the family controlling BMW, already holds 29 percent, Der Spiegel said. In January, BMW and SGL Carbon opened a joint venture in the United States in which they invested 100 million dollars in a high-tech plant to produce elements for BMW vehicles. In February, BMW\'s rival Volkswagen, took an eight-percent stake in SGL Carbon. \"If the price is right, we will increase our stake,\" a Volkswagen executive told Der Spiegel. Carmakers are taking an increasing interest in carbon fibre technology because of the combination of its strength and lightness. Based in Wiesbaden, in western Germany, SGL Carbon employs more than 6,000 people.