Tim Worstall had a post yesterday on the “peak oil” calculation, inspired by a long article in the Guardian. Tim makes the important point in this post and in an earlier one to which he links that the economic assumptions on which the calculation rests are too static to be realistic. They don’t recognize the phenomenon of substitutability and don’t make any allowance for/do any sensitivity analyses on cross-price elasticities of demand.
The comments on the post are also worth a read; note in particular the references to production capacity from oil sands in western Canada.
For more useful and insightful analysis, see Rob at Peak Oil Optimist.