I came across this neat website that tracks fuel consumption in the real World for Chevy Volts. You can use the spreadsheet to sort the data. For example the highest mileage Volt on the website is 368,818 miles and 128,344 of those miles were done using electricity.
Volt Stats interfaces with OnStar to collect data about the performance of Chevy Volts driving in the real world.
Interesting stats, so there are 2629 Volts on the road? That's quite rare, they were sold as the Vaxhaul Ampera here, but they stopped selling it due to it's unpopularity. There are about 1200 here in the UK I think. Weird to see some people are getting 32 MPG, and others are getting 15,000 MPG, what a difference!?
This kind of tracking is vital to determine real World range, Tesla do the same I believe, tracking over 1,000,000 electric miles by their owners every day.
GM sold around 100,000 Chevy Volts / Opel Amperas World wide. The few thousand on the site is probably the people who have OnStar and wanted their data published. Most higher spec new GMs come with OnStar and it is free for a year, after that it costs about $40/month. I think in order to have this data, you have to keep paying for OnStar.
The 15,000MPG is not a good representative for fuel usage for a plug in car. I think the MPGe is a better unit since it also includes the electricity used to move the vehicle. The best Volt is 108MPGe and the worst on this site is about 32MPGe.
The site also has the Spark EV, Bolt and the Cadillac ELR listed, just click on the different model.
" MPGe: Counts all electric miles driven as 93, 94 or 98 "MPGe", depending on the model year of the vehicle. See this wikipedia page for the gory details, but in short, 33.7 kw*hrs of energy has been determined to be equal to one gallon of gasoline, and the Volt is rated at a combined 93 MPGe (0.36 kw*hrs/mi) by the EPA for the 2011 model, 94 MPGe for 2012, 98 MPGe for 2013 and up, and 106 MPGe for 2016 and up. This gives a better account of the true energy usage of the vehicle, in a number that's easily comparable to traditional cars. However, this is just an estimation - I cannot currently read raw kw*hrs from Onstar, so actual energy usage could be better or worse than this number. Hopefully we can get a real MPGe calculation in the near future. The formula is: Total Miles / (Gallons Burned + (EV Miles / EPA rating))"