Before 1990, most car gas tanks were made of steel. By 1996 plastic had replaced steel in one out of four fuel tanks manufactured in North America. Last year plastic gas tanks had taken over an estimated 72% of the market in North America, and almost 50% worldwide. Automakers have been moving toward plastic for fuel tanks because the material is lighter in weight and more flexible to mold into the odd saddle-shaped tanks used in some vehicles today. Further clouding the fuel tank issue are stricter emissions regulations of the California Air Resources Board that go into effect in 2004. While not nationwide yet, some automakers are concerned that these requirements could influence national limitations on auto emissions. To meet the tougher standards, designers of plastic gas tanks opted for more complex multi-layer tanks that keep gasoline from seeping through the plastic into the atmosphere. At the same time, though, these many-layered tanks composed of multiple plastics bonded together may pose a problem when the car is junked and dismantled for recycling. The reason is that separating these different kinds of plastic is difficult. It's a lot easier for an auto dismantler to drain a steel tank and toss it into a pile of scrap for melting down by a steel recycler. While most of the cars with plastic fuel tanks are still on the road, in a few years many of these vehicles will be retired for good, presenting auto dismantlers -- the first line of recyclers in this industry -- with a major headache. "Those vehicles are now near the end of their life and raise both a question and a concern as to how to dispose of these plastic tanks," says Peter Mould, director of the Strategic Alliance for Steel Fuel Tanks, an industry trade group established by the American Iron & Steel Institute. "Right now they are only being landfilled. I'm not sure whether the recycling issue and the disposal issue are being addressed up front by the product designers." They are -- or at least at General Motors and Tier 1 automotive supplier Delphi Automotive Systems, they are. GM went so far as to conduct a careful study of plastic versus steel fuel tanks. In a study GM did with the University of Michigan, the company found that the two options -- considering the effort to mine and ship the iron ore that goes into steel and the process of making it versus that of plastic -- yield roughly the same amount of solid waste over the long run. "Our position is to look at the whole life cycle of the material and its environmental performance," Collum adds. "There isn't a clear-cut winner."