b'(3) The increase in proved reserves is a result of a 16 MMBbl increase associated in Jubilee related to the approval ofthe Greater Jubilee Full Field Development Plan (GJFFDP) and an 8 MMBoe increase associated with positiverevisions to the TEN fields.(4) The increase in purchase of minerals in place is related to Equatorial Guinea, representing the reserves associatedwith our equity method investment.(5) The increase in proved reserves is a result of a 10 MMBoe increase in Jubilee related to strong field performance,positive drilling results and increased estimate of original oil in place. Changes at TEN include a positive revisionof 4 MMBbl due to increased estimate of original oil in place, new drilling and development plan updates, and anegative revision of 3 MMBbl due to recovery factor adjustment from dynamic modeling. Changes at EquatorialGuinea are primarily a 4 MMBbl positive revision due to strong field performance at both Ceiba and OkumeComplex and a 6 MMBbl positive revision due to reservoir management strategies (re-opening shut-in wells,stimulations, surface/subsurface equipment installation).(6) The increase in purchase of minerals in place is related to the DGE acquisition completed in September 2018.Net proved reserves were calculated utilizing the twelve month unweighted arithmetic average ofthe first-day-of-the-month oil price for each month based on the respective benchmark price in theperiod January through December 2018. The average price is adjusted for crude handling,transportation fees, quality, and a regional price differential.Proved oil and gas reserves are defined by the SEC Rule 4.10(a) of Regulation S-X as thosequantities of oil and gas, which, by analysis of geoscience and engineering data, can be estimated withreasonable certainty to be commercially recovered under current economic conditions, operatingmethods, and government regulations. Inherent uncertainties exist in estimating proved reservequantities, projecting future production rates and timing of development expenditures.Capitalized Costs Related to Oil and Gas ActivitiesThe following table presents aggregate capitalized costs related to oil and gas activities:EquityMethodInvestmentU.S. Gulf of EquatorialGhana Mexico Other(1) Kosmos Total Guinea(2) Total(In thousands)As of December 31, 2018Unproved properties . $$ 318,831 $440,641 $ 759,472 $$ 759,472Proved properties . . . 3,191,157 1,045,3324,236,489 2,850,316 7,086,8053,191,157 1,364,163 440,641 4,995,961 2,850,316 7,846,277Accumulated depletion . (1,493,111) (57,986)(1,551,097) (2,717,020) (4,268,117)Net capitalized costs . . . $ 1,698,046 $1,306,177 $440,641 $ 3,444,864 $ 133,296 $ 3,578,160As of December 31, 2017Unproved properties . $ 55,179 $$409,930 $ 465,109 $$ 465,109Proved properties . . . 3,080,670 3,080,670 2,850,521 5,931,1913,135,849409,930 3,545,779 2,850,521 6,396,300Accumulated 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(1) Includes Africa (excluding Ghana) and South America.(2) Represents 50% interest in KTIPIs capitalized costs related to oil and gas activities.153'