Changes in the Standardized Measure for Discounted Cash Flows Equity Method Investment— Equatorial Ghana Guinea Total (In millions) Balance at December 31, 2014 . . . . . . . . . . . . . . $ 2,383 $ — $ 2,383 Sales and transfers 2015 . . . . . . . . . . . . . . . . . . (341) — (341) Net changes in prices and costs . . . . . . . . . . . . (2,842) — (2,842) Previously estimated development costs incurred during the period . . . . . . . . . . . . . . . . . . . . . 417 — 417 Net changes in development costs . . . . . . . . . . 6 — 6 Revisions of previous quantity estimates . . . . . . 375 — 375 Net changes in Ghanaian tax expenses(1) . . . . . 802 — 802 Accretion of discount . . . . . . . . . . . . . . . . . . . 341 — 341 Changes in timing and other . . . . . . . . . . . . . . 28 — 28 Balance at December 31, 2015 . . . . . . . . . . . . . . $ 1,169 $ — $ 1,169 Sales and transfers 2016 . . . . . . . . . . . . . . . . . . (191) — (191) Net changes in prices and costs . . . . . . . . . . . . (653) — (653) Previously estimated development costs incurred during the period . . . . . . . . . . . . . . . . . . . . . 225 — 225 Net changes in development costs . . . . . . . . . . 4 — 4 Revisions of previous quantity estimates . . . . . . 65 — 65 Net changes in Ghanaian tax expenses(1) . . . . . 143 — 143 Accretion of discount . . . . . . . . . . . . . . . . . . . 145 — 145 Changes in timing and other . . . . . . . . . . . . . . (61) — (61) Balance at December 31, 2016 . . . . . . . . . . . . . . $ 846 $ — $ 846 Purchase of minerals in place . . . . . . . . . . . . . . — 146 146 Sales and transfers 2017 . . . . . . . . . . . . . . . . . . (451) (16) (467) Extensions and discoveries . . . . . . . . . . . . . . . . 21 — 21 Net changes in prices and costs . . . . . . . . . . . . 485 — 485 Previously estimated development costs incurred during the period . . . . . . . . . . . . . . . . . . . . . 6 — 6 Net changes in development costs . . . . . . . . . . (388) — (388) Revisions of previous quantity estimates . . . . . . 415 — 415 Net changes in tax expenses(1) . . . . . . . . . . . . . (8) — (8) Accretion of discount . . . . . . . . . . . . . . . . . . . 98 — 98 Changes in timing and other . . . . . . . . . . . . . . (53) — (53) Balance at December 31, 2017 . . . . . . . . . . . . . . $ 971 $130 $ 1,101 (1) The Company is a tax exempt company incorporated pursuant to the laws of Bermuda. The Company has not been and does not expect to be subject to future income tax expense related to its proved oil and gas reserves levied at a corporate parent level. Accordingly, the Company’s Standardized Measure for the years ended December 31, 2017, 2016 and 2015, respectively, only reflect the effects of future tax expense levied at an asset level (in the Company’s case, future Ghanaian tax expense). 154