The idea of 'peak oil' - or the point in time when maximum petroleum extraction has been reached - is an idea which has been around since the 1950s. These days though, the debate centres on whether oil has or has not yet reached its 'peak', given that we have extracted so much of it, and that reserves are declining. But as new extraction techniques evolve - things like fracking, tar sands, deep water drilling - do we really have fuel that could last for centuries?