The history of plug-in hybrid electric vehicles (PHEVs) spans a little more than a century, but most of the significant commercial developments have taken place after 2002. The revival of interest in this automotive technology together with all-electric cars is due to advances in battery and power management technologies, and concerns about increasingly volatile oil prices and supply disruption, and also the need to reduce greenhouse gas emissions. Between 2003 and 2010 most PHEVs on the roads were conversions of production hybrid electric vehicles, and the most prominent PHEVs were aftermarket conversions of 2004 or later Toyota Prius, which have had plug-in charging and more lead-acid batteries added and their electric-only range extended.