To add a few more comments to what Greg outlined below, it's important to note that individual retailers of propane base their contracts with their suppliers on historical demand. They sign up either for variable-price contacts, or in some cases fixed-price contracts, based on what they estimate the demand from their customers will be for the season.
Last winter was an abnormal winter in terms of extreme cold temperatures. We saw across the country, as well as in the U.S., that there were a number of instances where retailers misjudged the amount of supply that they would need in terms of meeting their customers' demand for the winter. This led to, in some cases where suppliers didn't have fixed-price contracts with their wholesalers, paying escalated costs to ensure supply going forward.