Better analysis than I can provide is available at Eclectecon. It shows two things in “Marginal Cost of Oil Production”. The first is a chart of what prices are needed to justify the addition of new sources to global supply:
This just rehashes the last 10 years: we’ve reached a price that justifies extracting from shale (e.g., North Dakota) and tar sands (e.g., Alberta).
The second shows the shutdown prices based on country of origin.
The relevant values here are along the green line. This is how low the price can go before someone shuts down production. This suggests a floor of around $40. Demand decisions may force the price back up, but supply decisions are unlikely to until this level is hit.
One additional point is raised. Oil can be stored either above ground or still in the ground. Speculation that prices may be higher in the future might lead some to cut back production so as to store the oil in the ground. I don’t think this idea holds too much water: it’s basically a predatory pricing argument, and those don’t work as well in practice as many think they might.
Via Cold Spring Shops.