I don't run better fuel to see if it makes a difference, I run it because it does.
My 1986 D-250 I bought in 2003, since that day I always ran Amoco premium in it.
In this case the octane did make a mpg difference, it was an NA carbed intake.
In 2006 I had a fuel related problem and the mechanics had to tear apart the carb.
I was standing over the side when one of them said 'wow this carb is clean,' so I looked...
And it was, once inside the carb the metal parts were like brand new, super shiny, not a speck of gunk or dirt, I've never seen one that clean unless it was fresh out the box.
Wasn't the carb
Guess I could've told them that, but I don't back talk my mechanic.
I did tell them this:
Yes sir, I always run Amoco premium.
Once I switched I never looked back.
Even my lawn mower and my weed eater runs BP 93.
A FE gauge should be standard equipment in every vehicle.
Fifth and final mid-grade tank complete; 33.19MPG over 355 miles. Refilled with Shell regular.
Shell V-Power: 3400 miles and 100.074 gallons at 33.97 MPG.
Shell Mid-Grade: 3453 miles and 102.555 gallons at 33.67 MPG.
Random Regular: 3310 miles and 98.543 gallons at 33.59 MPG.
Capsule summary, using five fills for each section (dates are dates of fills):
11/20 - 12/11 Shell Mid-Grade: 1789 miles and 54.295 gallons at 32.95 MPG.
10/22 - 11/15 Shell V-Power: 1823 miles and 54.774 gallons at 33.28 MPG.
09/26 - 10/17 Random Regular: 1871 miles and 54.413 gallons at 34.39 MPG.
08/29 - 09/20 Shell Regular: 1687 miles and 49.69 gallons at 33.94 MPG.
08/06 - 08/27 Shell Mid-Grade: 1664 miles and 48.26 gallons at 34.48 MPG.
07/06 - 07/31 Shell V-Power: 1577 miles and 45.30 gallons at 34.81 MPG.
06/11 - 06/30 Random Regular: 1439 miles and 44.13 gallons at 32.61 MPG.
Given that currently mandated sulfur levels are roughly a tenth of what they were just a few years ago, recent data from an authoritative source would be appropriate.
The final gasoline sulfur rule was announced by President Clinton on December 21, 1999, and published formally a few weeks later (see 65 FR 6698; 2/10/00)... In 2006, specifications for gasoline content changed from the previous 500 ppm sulfur ceiling for RFG outside of California to a required 30 ppm annual average and a per-gallon cap of 80 ppm for most gasoline (with some delays for gasoline produced in the Rocky Mountain area or produced by small refiners).
Interesting information, however that is only a sulfur ceiling average on gasoline, other companys can still have lower average within the range.
My point is that things have changed drastically in recent years, so any statement regarding who has the highest (or lowest) sulfur content would need to be backed up by current data. Information from as little as a few years ago would no longer be germane.
There's also the question of whether variance within the newly mandated range is even significant.