Hi Octane

I had to whip out my cell phone and capture this nugget at a Burbank Valero station. The chain - now national, I believe - of gas stations proudly heralds the availability of "unlead" gasoline. What exactly happens to regular gasoline to make it "unlead"? Would the two extra characters used to form the more logical "unleaded" take up valuable gas pump real estate? Seems they have plenty to spare!