Strange, just notice for the 2019 S560 fuel capacity is 3.5 gallons more than the 450
 

Odd, I wonder why they both don't have the same tank? The Range is probably better on the S560 due to holding more fuel, maybe thats the deal breaker thats gonna make me get the S560 instead of the S450. I need a car with really good range. Makes me wonder though if it's possible that the S560 has a slightly smaller trunk due to the increased fuel tank capacity, if thats the case I will go with the S450, I really need as much trunk space as possible.

I think it's because S560 has less consumer friendly over S540 due to having a bigger engine .I remember my E250 came with a less smaller fuel tank but I had opted a bigger fuel tank which came as standard in E550s .In a nutshell, I wouldn't be surprised to see one could have a bigger fuel tank in their S450s for an extra cost .BMW doesn't offer that option only what it's available at the factory

Then I find here that it is indeed 24.6 for the S450?. https://www.media.mbusa.com/releases/2018-mercedes-benz-s450-sedan-s450-4matic-sedan-specifications?firstResultIndex=0&sortOrder=Publis hedAscending Yet, here it says 20.7. Anybody that has a S450, what really is the fuel tank capacity? Have you got more than 22 gallons into the car on a fill up? If so I guess it is 24.6. Reason I did this post is I find it hard to imagine MB would use different size tanks in the essentially the same bodied Sedan, it would make no sense.

Thats a good question. I have checked specs in several places and they all seem to vary from 20.7 gallons to 24.1 gallons. Right now I really don't know which is correct!

I'm thinking the 24.1 gallons is a mistake, that on both cars it is 20.7. Would be nice though if it was 24.1. Less fuel stops. Heck I'd take a 45 gallon tank if it were an option.

The only problem with that then is the fuel efficiency would drop. Gas is heavy, and the more gas you carry the more gas you spend carrying that weight...

So...yeah.