The EIA reports three different consumption numbers: Sales/deliveries by prime supplier, which is the one that Jay cited, retail sales by refiners, which you can find here:
http://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=pet&s=a403600001&f=a, and product supplied, which is here:
http://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=pet&s=mgaupus1&f=a
From reading the glossary, I get the impression that the best of these at approximating consumption of avgas is the product supplied table. It's the most consistent of the three tables as well. If you look at the retail sales by refiner, the volume has essentially gone to zero, apparently avgas is not being sold by the refiner any longer. I'm guessing that is why you saw the sales/deliveries by prime supplier move up, that was taking the place of the retail sales by refiner.
If you look at the product supplied chart, you'll see that the trend line is down, particularly over the last few years, where we saw declines of 8% - 9%. It looks like 2014's consumption will be off about 5% from 2013, so the decline has slowed. No doubt that some of this was commercial operator moving to turbine equipment, which I think has just about have to be done, as there aren't many working piston aircraft still in service. Look at FlightAware at various times of the day and week, you just don't see that many piston aircraft of the type that a commercial operator would use. Most of the time the most numerous type is either the Cirrus SR22 during the week, and 172s and 182s on the weekend.
I look at the trend line, and if I were an oil company executive and one of my product managers came by and suggested that we develop an unleaded avgas, I think I'd tell him no. Product supplied this year will be probably around 4.2 million barrels in 2014, and if the trend continues, will be in the low 3 million barrels per year by the end of the decade. By comparison, product supplied for jet fuel is staying steady at around 500 million barrels per year. At some point the volume isn't worth it to a major oil producer, and it becomes a boutique product and will be priced accordingly.
I've said a number of times on this board that I think it makes sense to move towards a dual fuel solution, mogas for the under 250 hp crowd, and some sort of jet fueled compression ignition engine for the higher horsepower folks, and a number of you have taken me to task for this. It's not that I want to see all the higher powered legacy aircraft grounded, it's that I think that is what is going to happen whether we like it or not. Cape Air, who operates one of the largest fleets of piston aircraft anywhere, is looking at Tecnam's P2012 as its replacement for its ancient Cessna fleet. The P2012 is powered by Lycoming's TEO-540, which is mogas capable.
All it represents is the accelerated depletion of finite natural resources, the vast majority of which will be converted to, and wasted as latent heat into the environment.
They say it's windy in Oklahoma because Texas sucks and Kansas blows! I know of at least 3 stations within 10 miles of my house that sell E0, no problem getting it around here. I only use it in the boat and lawn equipment though unless the price delta between E10 and E0 gets within about $.30/gal or so to make it worth it.
