We analyze alternative scenarios for future adoption of hydrogen fuel cell vehicles from 2015 to 2050. Our goal is to better understand the investment costs required to bring hydrogen and fuel cells to cost competitiveness and subsequent large scale use in the United States. We also estimate savings of greenhouse gas (GHG) emissions and gasoline consumption, relative to a “reference” case where no hydrogen fuel cells or other advanced technologies are implemented. Two hydrogen scenarios are considered: 1) Hydrogen fuel cell vehicles (FCVs) enter the market in 2015. They have 2.4 times the fuel economy and a $2000 higher learned-out cost than a comparable gasoline vehicle. By 2025, 10 million fuel cell vehicles are in the fleet, and by 2050, 67% of the fleet are FCVs. 2) Hydrogen and fuel cells are introduced more slowly. Hydrogen vehicles have twice the fuel economy and a $4000 higher learned-out cost than a comparable gasoline vehicle. By 2025, 2 million fuel cell vehicles are in the fleet, and by 2050, 20% of the fleet are FCVs. The hydrogen cases are compared to a reference case based on the EIA’s 2007 Annual Energy Outlook high oil price case, where gasoline vehicle fuel economy improves over time, but no hydrogen or other alternative fuels are implemented. We developed an EXCEL-based transition model to estimate the investments needed to introduce and subsidize hydrogen fuel cell vehicles and build hydrogen infrastructure during a transition. At each year, we specify the number of new hydrogen vehicles sold. A vehicle stock model is used to track the numbers of hydrogen and gasoline vehicles, and to find the fuel use and emissions each year. A steady-state hydrogen infrastructure model is used to estimate hydrogen fuel costs at different hydrogen demand levels. Initially, the first cost of the hydrogen FCV is much higher than the reference gasoline vehicle, but the FCV cost decreases over time, with cumulative production, manufacturing scale-up and learning. We conduct a cash flow analysis, considering the incremental first cost and fuel costs of hydrogen vehicles versus reference gasoline cars. Initially, the higher first cost of fuel cell vehicles leads to a negative cash flow, but eventually savings in fuel costs (due to the high efficiency of the fuel cell vehicle) outweigh the difference in vehicle costs, and the annual cash flow becomes positive. The cumulative investment cost to reach positive cash flow is found to be on the order of $10s of Billions. We also calculate oil use and GHG emissions associated with hydrogen scenarios, and compare these to other widely proposed strategies for sustainable transportation including improved energy efficiency of gasoline vehicles, and introduction of biofuels. We find that efficiency measures offer near-term reductions in greenhouse gases and oil use, and over a multi-decade time horizon, even greater reductions are possible with hydrogen from low carbon sources. This highlights the importance of both near term and long term strategies for reducing carbon emissions and oil use in the transportation sector.