what about competition? Surely, there will be some between exporters.

The important thing is to maximise profit - there will be competition, but that does not mean that they will produce more oil in the short term (or, more especially, enough oil to permit BAU economic growth) - profit means minimising cost/risk and maximising income. Profit is overridingly important to a producer, not the customer's/world's actual total needs.

The more efficiently a producer extracts oil the greater the depletion rate, the less time to make a profit - oil will be more expensive/difficult to extract in the future which is what causes global peak oil, since as prices rise (in order to make a profit) demand falls - as opposed to an individual oil well which peaks due to geological reasons.

Post peak we are in a new paradigm since, sadly, there appears to be no adequate alternative to oil for the forseeable future - on average expect constant declines in volume but constant increases in price - the lower the world total volume the higher the profit if you have an existing well. If the supernormal profits attract 'windfall' taxes there is a definite disincentive to produce.

Peak oil is bonanza time for producers but disaster time for consumers - the poorest consumers suffer the most - are people with the largest debts the richest or the poorest?

The economic theory, politics and energy sources used to run our 'exponential growth' world will have to be rethought I suspect.