at today's gasoline prices
and spread between regular and 93 octane premium
it may be that premium that HAS NO ADDED ETHANOL
might give a cost effective MPG increase

your tax $ paid for this EPA study of how
regular grade 87 octance gasoline heat content varies across the USA

http://www.epa.gov/orcdizux/rfgecon.htm

notice gasoline varies from 108,500 to 117,000 btu per gallon
so your MPG will be expected to vary about 9% too

The Bosch Automotive Handbook lists typical regular gasoline at
113,000
and premium gas at
118,000

toulene 126,650 (Formular One racecars used this when tank limit rules were in)

iso-octane 110,342 (100 Octane 'laboratory standard' gasoline is this pure chemical)

ethanol 75,900

acetone 80,700

if you buy yourself a digital scale
and weigh either exactly one gallon or one liter
the gasoline that weighs the most per volume (density)
usually has the most btu/gallon

your state's agriculture department may test gasoline
and if so will usually do one test per year for you
on octane and heat content
if you ask nicely

Standard Labs or Commercial Lab company
will do a commercial test for you for about $100 per test

 

The EPA claims a difference of 1.7% BTU/gal ... My instrumented results paint a far bleaker picture. I get far more than a 1.7% improvement with the winter blend here in Houston...

Toluene seemed like such a good idea, until I read the health risks associated with it.