The world's proven oil reserves at the end of 2006 stood at 1.208 trillion barrels, fractionally lower than 1.209 trillion at the end of 2005, BP warned in its Statistical view of World Energy published today.
The one billion-barrel reduction reflects in part a decline in Norway's reserves, which fell to 8.5 billion from 9.6 billion.
A BP official also said the overall 2006 figure could be revised once more data was available and that the original figure for 2005 had been 1.200 trillion barrels until an upward revision after more countries published reserve data.
Reserves in top oil producer Saudi Arabia rose to 264.3 billion barrels from 261.4 billion.
This year's review, which covers the period to end 2006, includes an assessment of the size of Canadian oil sands for the first time.
They stand at 163.5 billion barrels.