[mrfredward]

And so the difference between May and June futures should be constrained by the cost of storing oil for a month (the price of oil for June should be <= may + 1 month storage). Of course, storage facilities take time and money to build and shutdown, so there ends up being supply and demand based fluctuations for the cost of storing oil, and so if we run out of storage space (as happened at the end of April), you can get a huge difference in prices for futures that are a short time apart (which also happened at the end of April).