This report describes LBNL's approach for assessing uncertainty in any National Energy Modeling System (NEMS)-related analysis. Based on years of experience using LBNL-NEMS for various analyses, LBNL developed an alternative approach that aims to provide a simple yet comprehensive perspective of how the results behave under a given set of what we believe to be some of the issues important to large-scale energy modeling. This project has established a standard set of eight sensitivity cases that can be run overnight and are highly likely to produce stable and interesting results. The goal was to establish a limited number of interesting sensitivity cases that would routinely produce adjunct results to LBNL-NEMS reporting that will be of value to our readers. These cases will be routinely reported together with future LBNLNEMS results in the form of a standard output table. As an example, this work uses a Government Performance and Results Act (GPRA) analysis run as the baseline, but the goal is to establish a standardized set of cases that would change little over time and be applicable to other analyses in addition to GPRA. The approach developed here cannot serve as a substitute for a sensitivity analysis tailored to the question at hand, but it can provide a fast review of some areas that have proven to be of interest in the past.