At December 31, 2008, we had 664 mmboe of proved oil and gas reserves before royalties. This is a 10% decrease over the prior year. Including Syncrude, our total proved oil and gas and Syncrude reserves decreased 7% to 988 mmboe. The decrease resulted as additions from our capital program and positive technical revisions of previous estimates did not offset production and negative economic revisions from the decline in year-end oil and gas prices. On an after-royalty basis, our proved oil and gas reserves decreased 3% to 631 mmboe and increased 1% to 926 mmboe when including Syncrude reserves. The changes on an after-royalties basis reflect a reduction in royalties primarily at our oil sands projects where the royalties are sensitive to oil prices.

The following table provides a summary of the changes during 2008 in our proved oil and gas reserves (before royalties) excluding our Syncrude reserves. Refer to chapter Oil and Gas Producing Activities for proved reserves information on an after-royalties basis.

Excluding economic revisions, our net oil and gas reserve additions are 66 mmboe (60 after royalties) and including Syncrude are 74 mmboe (67 after royalties).

Extensions and discoveries of 34 mmboe (33 after royalties) are primarily from extending our Long Lake Project by core hole delineation, development drilling at Buzzard, and ongoing development of coalbed methane in Canada. Other increases relate to ongoing exploitation activities in the North Sea, Yemen, the Gulf of Mexico and Canada. No proved reserves will be recognized for exploration discoveries at Golden Eagle, Pink or Blackbird in the UK until we advance our understanding of these discoveries further and demonstrate a commitment to development.

Positive technical revisions of 32 mmboe (27 after royalties) are primarily from additions at Buzzard, Yemen and Canadian coalbed methane where drilling results and production performance supported higher reserve estimates. Negative technical revisions of 13 mmboe relate primarily to Ettrick where ongoing development drilling and testing did not support previous estimates.

Negative economic revisions of 50 mmboe (7 after royalties) are the result of lower commodity prices (primarily oil) and rising costs at year-end. Under SEC regulations, we are required to use year-end prices and costs to estimate our reserves. About 85% of this revision is price related, of which half occurred in our Canadian heavy oil properties, while the remaining changes occurred at our Buzzard, Ettrick, Scott and Telford fields in the UK, and some of our US shelf properties. The majority of the remaining revisions resulted from higher year-end costs, primarily on our Canadian heavy oil properties.

The following provides a summary of the changes in our proved oil and gas reserves (before royalties) excluding Syncrude, for the past three years. Refer to chapter Oil and Gas Producing Activities for proved reserves information on an after-royalties basis for the past three years.

Since the end of 2005, we added 440 mmboe (431 after royalties), sold 2 mmboe (2 after royalties) and produced 242 mmboe (191 after royalties). Extensions and discoveries of 134 mmboe (122 after royalties) occurred primarily at our Usan, Ettrick and Buzzard fields, Long Lake Project, Canadian coalbed methane, and the deep-water Gulf of Mexico. The net technical revisions of 89 mmboe (81 after royalties) include 78 mmboe (78 after royalties) of positive revisions in the UK primarily attributed to production performance at Buzzard and increased expected recoveries for our Long Lake Project based on analogous commercial SAGD projects. Negative technical revisions occurred primarily from lower-than-expected production performance at our Aspen field and some Shelf properties in the US Gulf of Mexico. Economic revisions of 205 mmboe (218 after royalties) are related to changes in year-end prices and costs. This includes a positive revision of 246 mmboe (245 after royalties) from reinstatement of Long Lake bitumen reserves that we had removed due to low bitumen prices at the end of 2004. This was partially offset by negative revisions of 41 mmboe (27 after royalties) as a result of substantial decline in oil and gas prices at December 31, 2008 versus 2005 and a rising cost environment that has not yet corrected with the decline in commodity prices.