You re comparing apples and oranges The CIA World Factbook is talking about proved reserves which are oil that has already been found whereas Campbell I believe the article doesn t cite its references completely enough to identify them is talking about ultimate reserves which is oil we might find but we haven t found it yet Neither is particularly useful unless you state what price you expect to get and what technology you expect to use And then there s the oil sands wild card Canada has 1 7 or so barrels of the stuff of which only 175 billion barrels are established which is yet another definition and Venezuela has similar sized reserves So basically it s comparing apples oranges bananas and watermellons