We determined materiality for the group to be $1 billion (2013 $1 billion), which represents 5% of underlying replacement cost profit (as defined on page 255) before tax having added back charges related to the Gulf of Mexico oil spill response. We used this measure to calculate our materiality to exclude the impact of both changes in crude oil and product prices and items disclosed as non-operating items that can significantly distort the results. This provides a basis for assessing the importance of misstatements and in determining the scope of our audit procedures.