Conventional oil peaked around 2005.  The increased production has come from more expensive and high carbon emissions unconventional oil (oil sands, fracking, deep water, Venezuela heavy oil etc.)   These cost more and have progressively lower EROIs.  

The reason for the current low price of oil is not real cost but increased production from fracked sources (mostly) which have yet to turn one positive dollar.

The reserves available to humanity are in the neighbourhood of 1.5 trillion bbls and we are using around 90 million a day.  90 x 365 = 33 billion bbl/year.  So around a 50 year lifespan of reserves with real costs getting progressively higher as more marginal reserves (higher hanging fruit) are exploited.

Economic theory is very hard to apply when printing presses are running overtime.  Best to change energy horses long before one runs out of steam and the other has yet to be born.

Cheers,
John Meyer