In the paper cup versus polyfoam cup example,the comparisons of operational data were fairly clean in the sense that one product’s environmental impact were almost always less than the other product’s.But,even here,there are some questions that can be raised .For example ,what is the cost of producing pentane emissions compared to the cost of water effluents and particulates?What are the economic benefits from recycling polyfoam cups?The advantage of assigning costs is that the total environmental costs provide an index that can be used for ranking the competing alternatives.How are costs assigned?