Life cycle assessment (LCA) evaluates the impact of the utilization and fate of resources (feedstocks, process energy and efficiency, and waste disposal) on various commercial products from a systems analysis perspective. Recently the use of LCA for estimating the greenhouse gas (GHG) emissions for liquid transportation fuels has received increased attention. LCA is an important tool for evaluating renewable fuel technologies and their effects on GHG emissions. Several international, national, and state initiatives are formulating policies and regulations based on published LCA studies for fossil and biomass-derived fuels. However, the application of LCA in transportation fuel sector is still an evolving science. Some principal parameters and their implications, such as direct and indirect land use change, methodologies for treating non-fuel byproducts, and the underlying uncertainties in the input data and assumptions, are not well understood and deserve systematic investigation. The present work uses the LCA of tallow-based renewable diesel fuel as a case study to show the impact of such parameters.