We modeled and conducted a parametric analysis of the US light-duty vehicle (LDV) stock to examine the impact of natural gas vehicles (NGVs) as they compete with electric vehicles, hybrids, and conventional powertrains. We find that low natural gas prices and sufficient public refueling infrastructure are the key drivers to NGV adoption when matched with availability of compressed natural gas powertrains from automakers. Due to the time and investment required for the build out of infrastructure and the introduction of vehicles by original equipment manufacturers, home natural gas compressor sales and bi-fuel NGVs serve as bridge technologies through 2030. By 2050, however, NGVs could comprise as much as 20% of annual vehicle sales and 10% of the LDV stock fraction. We also find that NGVs may displace electric vehicles, rather than conventional powertrains, as they both compete for consumers that drive enough miles such that fuel cost savings offset higher purchase costs. Due to this dynamic, NGVs in our LDV stock model offer little to no greenhouse gas emissions reduction as they displace lower emission powertrains. This finding is subject to the uncertainty in efficiency technology progression and the set of powertains and fuels considered.