Fuel poverty is a growing concern in France. Following the hike in energy prices that started in 2004, the problem of energy affordability for low-income households entered the political debate with the “Grenelle de l’environnement” in 2007. According to the standard UK definition (10% ratio) 3.4 million households were subject to fuel poverty in France in 2006. We question the way fuel poverty is currently measured and compare the impact of alternative measurement approaches on the extent and composition of fuel poverty in France. Then, we identify and characterize vulnerable households that are not ordinarily poor, but can be pushed into poverty because of their fuel bills. The incidence, depth and severity of poverty is measured with the Foster, Greer and Thorbecke indicator. Furthermore, econometric models are used to analyze which factors influence the probability of vulnerable households to fall into poverty. The study indicates that the proportion of fuel poor people and their characteristics differ significantly depending on the fuel poverty measure chosen. The econometric results show that the probability of falling into poverty is higher for those who are retired living alone, rent their home, use an individual boiler for heating, and cook with butane or propane.