Our browser extension (calasi dot com) displays fuel efficiency ratings of flights on Expedia (and more sites in the future). We help travelers find the lowest combination of price, duration and emissions, so when they have to fly at least they can make responsible choices. Interestingly efficient flights can be significantly more fuel efficient and yet be priced the same. So we just need to know which ones they are and then shift demand towards efficient routes. We released our public beta last month!