This excerpt taken from the AMZN 10-K filed Mar 11, 2005.
Asset Retirement Obligations
In accordance with SFAS No. 143, Accounting for Asset Retirement Obligations, we establish assets and liabilities for the present value of estimated future costs to return certain of our leased facilities to their original condition. Such assets are depreciated over the lease period into operating expense, and the recorded liabilities are accreted to the future value of the estimated restoration costs. Such amounts are not significant.
NOTES TO CONSOLIDATED FINANCIAL STATEMENTS(Continued)