Wholesale gas prices versus retail

For a few years now I’ve been wanting to keep track of the wholesale gas prices compared with the local retail prices.  It would be interesting to see the elasticity between the two.  It would also be interesting to track the deltas in price between Kernersville and Greensboro – some days there is a $0.14/gal spread while other times the prices may be identical.  Very curious as to why the spread changes in both of these data.

But to do track this information I’d have to keep track of it better and just haven’t had the time to put together a good way to track it.  Any suggestions?