These items are comprised of:

1. Mineral products, crude petroleum, and natural gas liquids
2. Supplies, parts, fuels, etc.

Beginning in 1982, respondents were asked to report their inventories at (the lower of) cost or market prior to adjustment to LIFO cost. This is a change from prior years in which respondents were permitted to value their inventories using any generally accepted accounting method. Therefore, 1982 through 2007 data for inventories are not strictly comparable to prior year data.

In addition, total beginning and end of year inventories are the sum of several different types of inventory valuations. Inventory valuation methods include:

1. Subject to Last-in, First-out (LIFO) costing (including LIFO reserve and value)
2. Not subject to LIFO costing
3. Valuation method not reported
4. Amount subject to LIFO reported without associated reserve and value