IE Questions: A What Tank?

We are hereby launching a new weekly Inside Energy series:

IE Questions! Yes, in these posts, we will be taking questions from our attractive and talented followers through email, social networking, carrier pigeon—whatever works. One of us will choose a question or two each week and doggedly track down the answer. Alas, we are early in this process, so for this installment I will be answering my own question. It’s one I didn’t even know I had until I was corrected.