> Those are still mostly dependent on fossil fuels, although they use less.

I don't think the word "mostly" belongs in that sentence - "partially" might work.

It depends significantly on how far you drive - I know 4 people with Plug-in hybrids. They all use ~0 fossil fuels most of the time, and only have to fill their gas tank when they go on a longer driving trip (roughly every 4-6 weeks or whatever). Considering how fuel inefficient city driving is, it's enough to eliminate at least half, maybe 2/3 of their fuel consumption.