COMSTOCK RESOURCES, INC. AND SUBSIDIARIES NOTES TO CONSOLIDATED FINANCIAL STATEMENTS — (Continued) The following table sets forth the changes in the standardized measure of discounted future net cash flows relating to proved reserves for the years ended December 31, 2011, 2012 and 2013: 2011 2012 2013 (Inthousands) Standardized Measure, Beginning of Year .......................... $606,136 $ 887,798 $ 641,325 Net change in sales price, net of production costs .................. 506 (217,925) 43,117 Development costs incurred during the year which were previously estimated ................................................ 205,418 179,549 187,643 Revisions of quantity estimates ................................ (50,399) (886,531) 48,411 Accretion of discount ........................................ 79,763 117,381 81,434 Changes in future development and abandonment costs ............. 10,962 628,088 (157,207) Changes in timing and other ................................... (58,304) 27,077 80,348 Extensions and discoveries .................................... 540,937 337,223 291,582 Purchases of minerals in place ................................. 2,959 — — Sales of minerals in place ..................................... — (236,925) — Sales, net of production costs .................................. (355,654) (307,407) (335,677) Net changes in income taxes ................................... (94,526) 112,997 (73,759) Standardized Measure, End of Year ............................... $887,798 $ 641,325 $ 807,217 F-31