Which airlines/flights are most fuel-efficient?
 

I've read that the Airbus 'neo' planes are more efficient, and also Norwegian's 787s. Does anyone know which other airlines/flights reliably use the more fuel-efficient planes?

Or are there other metrics you use when evaluating one flight's fuel efficiency over another?

The difference is more wether a plane is fully booked or not. A fully booked plane can be very efficient with about 3 l per 100 km per pax. 4 l per 100 km is about the average, which btw is still extremely low compared to taking a car. A bad flight comes to about 12 l per 100 km. The class you fly in also makes a huge difference. Other than that I'd only assume differences are marginal enough to be disregarded. Of course newer panes are more efficient, but wether you should book a Dreamliner vs an A380 is not something I would spend time thinking about in regards of doing good for the planet.

Which country (ies) are the worst per capita for flights? South Korea seems to get a new airline every other week, and they’re all for leisure. Not to mention, the single route with the most flights per day anywhere in the world - Seoul Gimpo to Jeju - hails out of the RoK.

Not that Western/other Asian countries are exculpated, but...

I don't own a car, so I put all my decision-making about carbon into flights (and alternatives). If I do have to fly somewhere, I want to maximize that decision, and, in purchasing my ticket, perhaps encourage the airlines that are prioritizing more fuel-efficient planes.

Here are a chart that could be useful to discussion of some aspects of the issue.

The chart is from an article of possible interest,
Does it matter to your carbon footprint whether you're flying across the Atlantic or the Pacific?
Posted Monday, 5 March 2018, 10:00 by Brandon Graver, ICCT / International Council on Clean Transportation
Link

Ryanair are pushing themselves as Europe's lowest emissions airlines.
(I can't post URL but here: corporate.ryanair.com slash environment)

Their measure is CO2 Per Pax/km - they say they manage to keep this lower than their competitors because of:

1. high load factor (96%)
2. young fleet (ave. of 6 years).

So while this makes them efficient they are still probably one of the biggest airline carbon emitters in Europe.

This Wikipedia page is very good:

Fuel economy in aircraft