Okay… so my headline was “catchy” to get you to read this post. Sorry, but I am a “victim” of the influence of Captain Kangaroo, Sesame Street and our Liberal Media 
Achilles,
I do not believe there is a “reserve” of fuel that will run out in 5 to 10 years. That’s not how the fuel production system works. Most gasoline you purchase is less than 30 days old. Aviation fuel is a little older but not more than 90 days.
The “problem” with 100LL is the additive, Tetrylethyl Lead. There is the belief that the EPA will mandate the phase out of leaded gasoline for off-road use in the next few years. The biggest issue is that only a few companies (I think only two, maybe only one) make the additive (Tetrylethyl Lead) and they see a declining market. It’s also expensive to manufacture and the class action lawyers are looking into the stuff as part of the lead paint litigation that is being bandied about (a suit was filed in Maryland over lead additives).
The use of lead additive in gasoline goes back to 1924… it’s an interesting story of corporate intrigue that conspiracy theorists love to talk about. (Prescott Bush, Sr. (yeah, the family tree of our prez), Saudi Pipelines, providing Tetrylethyl Lead to the Nazi’s for the European Invasion, etc.)
For an interesting yet possibly flawed report on the history of lead as an additive, follow this link:
http://www.voicemedia.net/Secrethistoryoflead.pdf
(sorry, nothing about the Bush scandal in this one though you can find it on the web with a Google search on Prescott Bush, Sr., Conspiracy and perhaps Skull and Bones. BTW, I have not done enough research on this stuff (conspiracy theory) to form an educated opinion. I have more interesting things to learn about first and include the reference only as an invite for you to become more educated on the issue before forming an opinion. And, as Jim Fallows might admonish me, I have to tie the headline into the story in some manner!)
However, NASCAR is still a big user of leaded gasoline (must be something good about it) getting fuel up to 112 octane. So perhaps as long as NASCAR is popular we can get our lead we love so dearly.
On a more positive note, we are blessed to live in a capitalistic society where it is in someone’s best interest (economically) to find an alternative fuel or solution. As a result of this blessing we will all benefit as well and I believe we will find this debate to be interesting, but not relevant.
Mark
Ps - If you believe, after doing your resaearch, that the purchase of a piston powered airplane is a poor choice, then by all means do not purchase one. It may not be in your best interest to do so. After researching the subject, I have come to the conclusion that it is in my best interest to purchase one. If I have to buy a different engine (diesel, fussion, fuel cell, fission, etc) in 5 years, that is okay with me as well.
Therefore, if you are an entrepreneur and wish to invest your resources (time and money) in finding a superior alternative for 100LL, then I shall be pleased to join thousands of airplane owners in making you fabulously wealthy by purchasing your product. It’s my way of saying “thanks” for a job well done!