Cost basis on sales of rights for capital gains tax

In November 2015 we sold mineral rights in Grady Co. OK, and now need to come up with a cost basis to determine the capital gains for IRS 2015 income tax. One person told me to find out the pooling order price per acre on or about the date we acquired the property, then multiply that figure by 3. My question for the Mineral Rights Forum community is: how do I find out the pooling order price per acre for (in this case) August 9, 1988? From the Corporation Commission? Any advice or guidance would be appreciated!

Your cost basis depends on (1) how you acquired the mineral rights and (2) how much depletion you have taken since 1988. 1988 Acquisition Basis: If you purchased the minerals, then it is the purchase price. If the minerals were a gift, then you get the previous owner's basis. If you inherited the minerals, then it is the value at the date of death. Reduction in Basis Since 1988: If you have received royalties since 1988, then you must reduce your acquisition basis, dollar for dollar, for the total depletion over the years. However, your depleted basis is not reduced below zero.