Plug-In Hybrids Up to Four Times Less Fuel Efficient in Real Life, Study Says 29 Apr 2021, 20:37 UTC · by For years seen as the perfect solution for easing people into the upcoming electric car future, plug-in hybrid (PHEV) cars are not used as they should. That results in extraordinary differences in fuel economy and emissions between real-life driving and laboratory tests. 1 photo According to German researchers, PHEVs use more fossil fuels and emit up to four times more carbon dioxide in the real world, and it all comes down to drivers not using the cars’ electric motors as much as they should.