(Also called Accumulated Depletion.) The portion of the cost of acquiring and putting into production a natural asset (e.g., oil wells, gold mines) that has been written off against income (expensed). A balance sheet account showing the amount of the cost of a natural wasting asset that has been charged against income. For example: Gold mine, at cost $100,000 Less: Allowance for Depletion 25,000 Net Book Value $ 75,000