proved reserves can be added as expansions are permitted , funding is approved and certain stipulations of the joint venture agreement are satisfied .the following table sets forth changes in estimated quantities of net proved bitumen reserves for the year 2008 .estimated quantities of proved bitumen reserves ( millions of barrels ) 2008 .
[['( millions of barrels )', '2008'], ['beginning of year', '421'], ['revisions ( a )', '-30 ( 30 )'], ['extensions discoveries and additions', '6'], ['production', '-9 ( 9 )'], ['end of year', '388']]
( a ) revisions were driven primarily by price and the impact of the new royalty regime discussed below .the above estimated quantity of net proved bitumen reserves is a forward-looking statement and is based on a number of assumptions , including ( among others ) commodity prices , volumes in-place , presently known physical data , recoverability of bitumen , industry economic conditions , levels of cash flow from operations , and other operating considerations .to the extent these assumptions prove inaccurate , actual recoveries could be different than current estimates .for a discussion of the proved bitumen reserves estimation process , see item 7 .management 2019s discussion and analysis of financial condition and results of operations 2013 critical accounting estimates 2013 estimated net recoverable reserve quantities 2013 proved bitumen reserves .operations at the aosp are not within the scope of statement of financial accounting standards ( 201csfas 201d ) no .25 , 201csuspension of certain accounting requirements for oil and gas producing companies ( an amendment of financial accounting standards board ( 201cfasb 201d ) statement no .19 ) , 201d sfas no .69 , 201cdisclosures about oil and gas producing activities ( an amendment of fasb statements 19 , 25 , 33 and 39 ) , 201d and securities and exchange commission ( 201csec 201d ) rule 4-10 of regulation s-x ; therefore , bitumen production and reserves are not included in our supplementary information on oil and gas producing activities .the sec has recently issued a release amending these disclosure requirements effective for annual reports on form 10-k for fiscal years ending on or after december 31 , 2009 , see item 7 .management 2019s discussion and analysis of financial condition and results of operations 2013 accounting standards not yet adopted for additional information .prior to our acquisition of western , the first fully-integrated expansion of the existing aosp facilities was approved in 2006 .expansion 1 , which includes construction of mining and extraction facilities at the jackpine mine , expansion of treatment facilities at the existing muskeg river mine , expansion of the scotford upgrader and development of related infrastructure , is anticipated to begin operations in late 2010 or 2011 .when expansion 1 is complete , we will have more than 50000 bpd of net production and upgrading capacity in the canadian oil sands .the timing and scope of future expansions and debottlenecking opportunities on existing operations remain under review .during 2008 , the alberta government accepted the project 2019s application to have a portion of the expansion 1 capital costs form part of the muskeg river mine 2019s allowable cost recovery pool .due to commodity price declines in the year , royalties for 2008 were one percent of the gross mine revenue .commencing january 1 , 2009 , the alberta royalty regime has been amended such that royalty rates will be based on the canadian dollar ( 201ccad 201d ) equivalent monthly average west texas intermediate ( 201cwti 201d ) price .royalty rates will rise from a minimum of one percent to a maximum of nine percent under the gross revenue method and from a minimum of 25 percent to a maximum of 40 percent under the net revenue method .under both methods , the minimum royalty is based on a wti price of $ 55.00 cad per barrel and below while the maximum royalty is reached at a wti price of $ 120.00 cad per barrel and above , with a linear increase in royalty between the aforementioned prices .the above discussion of the oil sands mining segment includes forward-looking statements concerning the anticipated completion of aosp expansion 1 .factors which could affect the expansion project include transportation logistics , availability of materials and labor , unforeseen hazards such as weather conditions , delays in obtaining or conditions imposed by necessary government and third-party approvals and other risks customarily associated with construction projects .refining , marketing and transportation refining we own and operate seven refineries in the gulf coast , midwest and upper great plains regions of the united states with an aggregate refining capacity of 1.016 million barrels per day ( 201cmmbpd 201d ) of crude oil .during 2008 .

Question: by how much did proved bitumen reserves decrease during 2008?
Answer: -7.8%