.
supplementary information on oil and gas producing activities ( unaudited ) changes in the standardized measure of discounted future net cash flows ( in millions ) 2011 2010 2009 .
what was the average net annual change in discounted future net cash flows ( in millions ) for the years 2011 , 2010 , and 2009?
( in millions ) the net change for the year of 2011 is 4648 ; the net change for the year of 2010 is 3625 ; the net change for the year of 2009 is 1620 ;
( in millions ) 2011 2010 2009
sales and transfers of oil and gas produced net of production and administrative costs $ -7922 ( 7922 ) $ -6330 ( 6330 ) $ -4876 ( 4876 )
net changes in prices and production and administrative costs related to future production 12313 9843 4840
extensions discoveries and improved recovery less related costs 1454 1268 1399
development costs incurred during the period 1899 2546 2786
changes in estimated future development costs -1349 ( 1349 ) -2153 ( 2153 ) -3773 ( 3773 )
revisions of previous quantity estimates 2526 1117 5110
net changes in purchases and sales of minerals in place 233 -20 ( 20 ) -159 ( 159 )
accretion of discount 2040 1335 787
net change in income taxes -6676 ( 6676 ) -4231 ( 4231 ) -4345 ( 4345 )
timing and other 130 250 -149 ( 149 )
net change for the year 4648 3625 1620
beginning of the year 9280 5655 4035
end of year $ 13928 $ 9280 $ 5655