If the demand doesn't support it, it doesn't matter. It is an attempt to hide part of the price but there are people who are price-sensitive and every dollar matters to some. If it pushes two many people away then it isn't supported. Only Delta will ever know those numbers but rest assured they do.

Signaling? I paid UA a fuel surcharge last month.

Maybe its signaling an increased fuel surcharge. Or maybe they are just matching United.

I just booked a Delta flight one way to BOI this summer in the main cabin for a family of 4. Got a decent fare. Not sure if a fuel surcharge was added to it.

Just looked at my receipts. Paid DL a $520 fuel surcharge in January. Paid UA a $520 fuel charge in February. I have an upcoming trip on DL and paid a $550 fuel surcharge.

All are TATL flights

They don't have fuel surcharges/carried-imposed fees on domestic fares.

Checked receipt for DAY-VIE trip last year for August 2021 trip (main cabin V fares) which cost around $700 roundtrip. Base fare was $71.50 each way and YR surcharge was $200 each way. Checked route for August flights this year and roundtrip main cabin V fares are now going for around $1400 total with base fare of $427.50 each way and exact same YR surcharge of $200 each way. So the 100% price increase is entirely due to base fares going up and not YR surcharge increases. YR surcharges (the airlines now call them carrier-imposed surcharges rather than "fuel surcharges") set a bit of a floor for ticket prices, but they really don't have that much to do with what you ultimately pay as that is largely driven by supply and demand.

They do currently have main cabin V fares for about $866 roundtrip total on this route ($153.50 base fare each way) for travel through May, so those August V fares may get discounted if demand is not as robust as they currently seem to be expecting.

That was a quote from the article.

No one has paid a fuel surcharge this year (yet). YR hasn't been a fuel fee for years.

DL refers to both YQ and YR as carrier-imposed surcharges rather than fuel surcharges -- https://www.delta.com/us/en/booking-...taxes-and-fees
So they don't currently seem to have any codes which are strictly listed as "fuel surcharges". Looking at older and NW and DL email receipts, they both used to be coded as YQ and then DL switched to YR sometime between 2012 and 2014. Currently for US-EU tickets, each-way YR surcharges are currently generally $200 for BE/MC/C+, $300 for PS, and $800 for D1. But there are some JFK-LHR BE fares which have $110 each-way surcharge.

Here's a few select each-way YQ/YR surcharges going back to 2005 for US-EU coach fares I pulled from email receipts.

3/14/05 $25
3/24/06 $55
10/27/06 $65
1/18/07 $60
4/14/08 $85
1/31/09 $112
1/5/12 $220
11/22/16 $100
7/11/21 $200