Part of the capital costs actually incurred up to the date of reserves estimation minus depreciation and amortization expenses. Items such as exploration costs, land acquisition costs, and costs of financing can be included. A sunk cost is a cost that has already been incurred, and therefore cannot be avoided by any strategy going forward. The term refers to costs that have already been incurred and which cannot be reimbursed, such as a natural gas pipeline that has already been constructed becomes a sunken cost, because even if no gas flows through it the cost of the laying of the pipeline has been sunken or lost regardless. Sunk cost can represent the sum of all past costs incurred, including embedded costs and capital costs, but it does not include labor, rental, maintenance or other ongoing charges for things required in the present