Recently, we’ve heard a lot about new sanctions the U.S. government may impose on the Iranian economy—in particular, against Iranian oil. Sanctions are a common policy tactic, but how do they work from an economic perspective?

First consider the supply of oil, which economists have described as a “global bathtub“: The tub is filled by “spigots” from various suppliers and depleted by “drains” from various consumers. The global oil price is determined by the sum of these supplies and demands for oil. The graph above shows global oil prices for West Texas Intermediate, Brent, and Dubai crude oil. We can see their global prices are fairly similar over time, with small differences between them. (Read this 2016 FRED Blog post for more info on these slight, temporary price differences between types of oil.)

The idea behind a global price for oil is the “law of one price” in international trade: If a homogenous good has negligible transportation or transaction costs, its price should be the same in all markets. This holds for crude oil, although not for a consumer good like a Big Mac, for example. Given that the global oil market is an integrated market, a shortfall in one region can be adjusted for by shipping the same or similar oil from another region in the world.

Now, what if a country is targeted by a ban on oil exports, as Iran was in 2012? The graph below show Iran’s oil production and oil exports, with noticeable declines beginning in 2012 that contributed to its 15-20% decline in per capita GDP. The last graph shows how the U.S. stopped importing oil from Iran, with the value of U.S. imports dropping to almost zero in 2012-15. Note: We can’t conclude from these data that the sanctions affected the price of Iranian oil, only that there was a decline in the quantity produced.

So why did these sanctions work in reducing oil exports from Iran? Economists say these sanctions were effective because of the international coalition that included key Asian countries that are heavy importers of oil. As for the global price of oil, it was fairly consistent in 2012-15, without any substantial changes. More FRED data series show how U.S. oil production has increased since 2012, compensating for the decline in production levels of other countries during that time. So, U.S. oil acted as a substitute for Iranian oil during this period and helped keep global oil prices stable. Exactly what we’d expect given the law of one price.

How these graphs were created: Search for “global price crude” (first graph) and “crude oil Iran” (second graph), select the series, and click “Add to Graph.” For the third graph, search for and select “goods imports Iran” and click “Add to Graph.”

Suggested by Suvy Qin and George Fortier.