Production alternatives for single-walled carbon nanotubes (SWCNT) such as chemical vapor deposition, laser, arc and flame, vary widely in material and energy yields, catalyst requirements and product characteristics. The overall environmental profile must be assessed relative to performance in a specific end-use application, such as lithium ion batteries for electric or plug-in hybrid vehicles. Although in general SWCNT have several properties that make them attractive for transportation applications, production is a material- and energy-intensive process. High-yield synthesis pathways may be environmentally inefficient if extensive purification is required. Life cycle assessment (LCA) is an approach to quantifying the environmental tradeoffs engendered by technology substitution. However, it is essential to recognize that the results of LCA for one type of SWCNT may not be applicable to SWCNT of different purity, length, diameter, chirality or conductivity. This paper discusses sources of variability and uncertainty in production of SWCNT and makes several recommendations with regard to LCA of nanomaterials.