Principal Sources of Changes in Discounted Cash Flows

Years ended December 31 (millions of C$) 2010 2009 2008
Sales of oil and gas produced net of production costs (4,834) (4,280) (7,562)
Net change in prices 4,635 4,901 (15,881)
Net change in transportation costs (203) 223 (73)
Net changes in production costs 402 (706) (1,049)
Net changes in future development and site restoration costs (28) (710) (842)
Development costs incurred during year 1,651 1,677 2,066
Extensions, discoveries and improved recovery 2,049 1,062 708
Revisions of previous reserves estimates 700 406 (141)
Net purchases 194 17 33
Net sales of reserves in place (919) (807) (371)
Accretion of discount 1,132 832 2,839
Net change in taxes (2,526) (1,460) 9,930
Other 29 (82) 682
Net change 2,282 1,073 (9,661)