(3) The unweighted arithmetic average first-day-of-the-month prices for the prior 12 months was $54.42 for Dated Brent at December 31, 2017. The price was adjusted for crude handling, transportation fees, quality, and a regional price differential. These adjustments are estimated to include a $0.10 premium, a $0.02 premium and a $0.53 discount relative to Dated Brent for the Jubilee Field, TEN fields and our equity method investment, respectively. The adjusted price utilized to derive the Jubilee Field PV-10, TEN PV-10 and equity method investment PV-10 is $54.52, $54.44 and $53.89, respectively. (4) Future net revenues and PV-10 have been adjusted from the reserve report which is based on the entitlements method as we account for oil and gas revenues under the sales method of accounting. Estimated proved reserves Unless otherwise specifically identified in this report, the summary data with respect to our estimated net proved reserves for the years ended December 31, 2017, 2016 and 2015 has been prepared by Ryder Scott Company, L.P. (‘‘RSC’’), our independent reserve engineering firm for such years, in accordance with the rules and regulations of the Securities and Exchange Commission (‘‘SEC’’) applicable to companies involved in oil and natural gas producing activities. These rules require SEC reporting companies to prepare their reserve estimates using reserve definitions and pricing based on 12-month historical unweighted first-day-of-the-month average prices, rather than year-end prices. For a definition of proved reserves under the SEC rules, see the ‘‘Glossary and Selected Abbreviations.’’ For more information regarding our independent reserve engineers, please see ‘‘—Independent petroleum engineers’’ below. Our estimated proved reserves and related future net revenues, PV-10 and Standardized Measure were determined using index prices for oil, without giving effect to derivative transactions, and were held constant throughout the life of the assets. Future net revenues represent projected revenues from the sale of proved reserves net of production and development costs (including operating expenses and production taxes). Such calculations at December 31, 2017 are based on costs in effect at December 31, 2017 and the 12-month unweighted arithmetic average of the first-day-of-the-month price for the year ended December 31, 2017, adjusted for anticipated market premium, without giving effect to derivative transactions, and are held constant throughout the life of the assets. There can be no assurance that the proved reserves will be produced within the periods indicated or prices and costs will remain constant. Independent petroleum engineers Ryder Scott Company, L.P. RSC, our independent reserve engineers for the years ended December 31, 2017, 2016 and 2015, was established in 1937. For over 75 years, RSC has provided services to the worldwide petroleum industry that include the issuance of reserves reports and audits, appraisal of oil and gas properties including fair market value determination, reservoir simulation studies, enhanced recovery services, expert witness testimony, and management advisory services. RSC professionals subscribe to a code of professional conduct and RSC is a Registered Engineering Firm in the State of Texas. For the years ended December 31, 2017, 2016 and 2015, we engaged RSC to prepare independent estimates of the extent and value of the proved reserves of certain of our oil and gas properties. These reports were prepared at our request to estimate our reserves and related future net revenues and PV-10 for the periods indicated therein. Our estimated reserves at December 31, 2017, 2016 and 2015 and related future net revenues and PV-10 at December 31, 2017, 2016 and 2015 are taken from reports prepared by RSC, in accordance with petroleum engineering and evaluation principles which RSC believes are commonly used in the industry and definitions and current regulations established by 26