We sell a limited amount of product under short-term price agreements or at prevailing market rates. The majority of our revenues are realized through long-term take-or-pay contracts. The expiration dates of these contracts range from 2016 through 2020; however, certain contracts include extension periods, as defined in the respective contracts. These agreements define, among other commitments, the volume of product that our customers must purchase, the volume of product that we must provide and the price that we will charge and that our customers will pay for each ton of contracted product. Prices under these agreements are generally either fixed or indexed to WTI and subject to adjustment, upward or downward, based upon: (i) certain changes in published producer cost indices, including the Consumer Price Index for All Urban Consumers and the Producer Price Index published by the U.S. Bureau of Labor Statistics; or (ii) market factors, including a natural gas surcharge and a propane surcharge which are applied if the Average Natural Gas Price or the Average Quarterly Mont Belvieu TX Propane Spot Price, respectively, as listed by the U.S. Energy Information Administration, are above the benchmark set in the contract for the preceding calendar quarter. As a result, our realized prices may not grow at rates consistent with broader industry pricing. For example, during periods of rapid price growth, our realized prices may grow more slowly than those of competitors, and during periods of price decline, our realized prices may outperform industry averages. With respect to the take-or-pay arrangements, if the customer is not allowed to make up deficiencies, we recognize revenues to the extent of the minimum contracted quantity, assuming payment has been received or is reasonably assured. Such revenue is generally recognized either quarterly or at the end of a customer contract year rather than ratably over the respective contract year. If deficiencies can be made up, receipts in excess of actual sales are recognized as deferred revenues until production is actually taken or the right to make up deficiencies expires.