This investigation examines the economics of producing electricity from proton-exchange membrane (PEM) fuel cell systems under various conditions, including the possibility of using fuel cell vehicles (FCVs) to produce power when they are parked at office buildings and residences. The analysis shows that the economics of both stationary fuel cell and FCV-based power vary significantly with variations in key input variables such as the price of natural gas, electricity prices, fuel cell and reformer system costs, and fuel cell system durability levels. The "central case" results show that stationary PEM fuel cell systems can supply electricity for offices and homes in California at a net savings when fuel cell system costs reach about $6000 for a 5 kW home system ($1200/kW) and $175,000 for a 250 kW commercial system ($700/kW) and assuming somewhat favorable natural gas costs of S6/GJ at residences and S4/GJ at commercial buildings. Grid-connected FCVs in commercial settings can also potentially supply electricity at competitive rates, in some cases producing significant annual benefits. Particularly attractive is the combination of net metering along with time-of-use electricity rates that allow power to be supplied to the utility grid at the avoided cost of central power plant generation. FCV-based power at individual residences does not appear to be as attractive, at least where FCV power can only be used directly or banked with the utility for net metering and not sold in greater quantity, due to the low load levels at these locations that provide a poor match to automotive fuel cell operation, higher natural gas prices than are available at commercial settings, and other factors. (C) 2002 Elsevier Ltd. All rights reserved.