Inventories consisted primarily of bulk ethanol, specialty alcohols, corn, co-products, low-carbon and Renewable Identification Number (“RIN”) credits and unleaded fuel, and are valued at the lower-of-cost-or-net realizable value, with cost determined on a first-in, first-out basis. Inventory is net of a $2,678,000 valuation adjustment as of December 31, 2017. Inventory balances consisted of the following (in thousands):