Many Tulsans have taken notice of a change in their fuel economy in recent months.

Of course, many different factors can impact fuel economy - air pressure in tires, temperature of the fuel, driving habits, etc.

But an indisputable difference in the fuel efficiency in your car or truck is the introduction of corn-based ethanol in your gasoline.

Nearly all Tulsa-area gas retailers are now pumping so-called E10 fuel - that is a mixture of 90-percent traditional gasoline and 10-percent corn-based ethanol.

The math is pretty clear that you're now spending more money on less energy:

One gallon gas = 115,000 BTU

One gallon ethanol = 76,000 BTU

One gallon E10 = 111,100 BTU

(A BTU is British Thermal Unit - it's a measure of energy content)

The difference between the BTUs of pure gasoline and the E10 is about 3.4-percent. That means that you're getting about 3.4-percent less efficiency with the use of E10.

If E10 proves to reduce fuel economy, why do we use it?

In Part I of our series "What's in your Gas?" we talk with QuikTrip's Mike Thornbrugh and learn why QT, and nearly every other gas retailer in Green Country, pumps E10.

In Part II of our series, we explore whether or not retailers should be compelled by law to label the fuel ingredients so that you will know what you're pumping into your car when you fill up.

Have you noticed a decrease in your fuel efficiency?

Should all retail gas pumps be labeled with fuel content?