The first commercially available plug-in hybrid electric vehicle (PHEV), the General Motors (GM) Volt, was introduced into the market in mid-December 2010. The Volt uses a series-split powertrain architecture, which provides benefits over the series architecture that typically has been considered for use in electric-range extended vehicles (EREVs). A specialized EREV powertrain, called the Voltec, drives the Volt through its entire range of speed and acceleration with battery power alone and within the limit of battery energy, thereby displacing more fuel with electricity than a PHEV, which characteristically blends electric and engine power together during driving. This paper assesses the benefits and drawbacks of these two different plug-in hybrid electric architectures (series versus series-split) by comparing component sizes, system efficiency, and fuel consumption over urban and highway drive cycles. Based on dynamic models, a detailed component control algorithm was developed for each PHEV. In particular, for the GM Voltec, a control algorithm was proposed for both electric machines to achieve optimal engine operation. The powertrain components were sized to meet all-electric-range, performance, and grade capacity requirements. This paper presents and compares the impact of these two different powertrain configurations on component size and fuel consumption.