(3) The increase in proved reserves is a result of a 2 MMBbl increase associated with in-fill drilling results and a 10 MMBbl increase associated with field performance for Jubilee partially offset by 2 MMBbl of negative revisions to the TEN fields due to decreased pricing. (4) The increase in proved reserves is a result of an 8 MMBbl increase associated with positive revisions to the TEN fields as a result of the completion of seven wells along with the initiation of TEN production partially offset by 1 MMBbl of negative revisions to the Jubilee Field due to decreased pricing. (5) The increase in proved reserves is a result of a 16 MMBbl increase associated in Jubilee related to the approval of the Greater Jubilee Full Field Development Plan (GJFFDP) and an 8 MMBoe increase associated with positive revisions to the TEN fields. (6) The increase in purchase of minerals in place is related to Equatorial Guinea, representing the reserves associated with our equity method investment. Net proved reserves were calculated utilizing the twelve month unweighted arithmetic average of the first-day-of-the-month oil price for each month for Brent crude in the period January through December 2017. The average 2017 Brent crude price of $54.42 per barrel is adjusted for crude handling, transportation fees, quality, and a regional price differential. Based on the crude quality, these adjustments are estimated to be $0.10 premium, $0.02 premium and $0.53 discount per barrel for Jubilee, TEN and our equity method investment, respectively; therefore, the adjusted oil price is $54.52, $54.44 and $53.89 per barrel for Jubilee, TEN and our equity method investment, respectively. Proved oil and gas reserves are defined by the SEC Rule 4.10(a) of Regulation S-X as those quantities of oil and gas, which, by analysis of geoscience and engineering data, can be estimated with reasonable certainty to be commercially recovered under current economic conditions, operating methods, and government regulations. Inherent uncertainties exist in estimating proved reserve quantities, projecting future production rates and timing of development expenditures. Capitalized Costs Related to Oil and Gas Activities The following table presents aggregate capitalized costs related to oil and gas activities: Equity Method Investment— Kosmos Equatorial Ghana Other(1) Total Guinea(2) Total (In thousands) As of December 31, 2017 Unproved properties . . . $ 55,179 $409,930 $ 465,109 $ — $ 465,109 Proved properties . . . . . 3,080,670 — 3,080,670 2,850,521 5,931,191 3,135,849 409,930 3,545,779 2,850,521 6,396,300 Accumulated depletion . . (1,234,806) — (1,234,806) (2,678,897) (3,913,703) Net capitalized costs . . . . $ 1,901,043 $409,930 $ 2,310,973 $ 171,624 $ 2,482,597 As of December 31, 2016 Unproved properties . . . $ 347,950 $571,106 $ 919,056 Proved properties . . . . . 2,771,779 — 2,771,779 3,119,729 571,106 3,690,835 Accumulated depletion . . (989,946) — (989,946) Net capitalized costs . . . . $ 2,129,783 $571,106 $ 2,700,889 (1) Includes Africa, excluding Ghana, Europe and South America. (2) Represents 50% interest in KTIPI’s capitalized costs related to oil and gas activities. 150