Reserve Currencies and Why the Dollar Dominates

Why so much of the world's trade and savings runs through the US dollar, even for transactions that have nothing to do with the United States.

Picture a company in Brazil buying machine parts from a supplier in Vietnam. Neither country is the United States, yet there’s a strong chance that transaction is priced, invoiced, and settled in US dollars rather than Brazilian reais or Vietnamese dong. This isn’t an accident or a leftover colonial arrangement - it reflects the dollar’s role as the world’s leading reserve currency: a currency that governments, central banks, and businesses around the world widely hold and use for international trade and savings, even when neither party to a given deal is American.

What makes a currency a reserve currency

Central banks around the world hold foreign exchange reserves - stockpiles of foreign currency, mostly held in the form of government bonds - specifically to manage their own currency’s value, pay for imports during a crisis, and reassure markets they can meet foreign debt obligations if needed. For decades, the majority of global foreign exchange reserves have been held in US dollars, far more than any other single currency, which is the clearest evidence of the dollar’s reserve status.

A handful of features tend to make a currency attractive for this role: the issuing country needs a large, stable economy; deep and liquid financial markets where huge sums of that currency can be bought and sold without dramatically moving the price; reliable rule of law and property rights, so foreign holders trust their money won’t simply be seized; and enough global trust that other countries are willing to hold large reserves in it rather than their own currency. The US dollar has checked all of these boxes since the Bretton Woods system, covered earlier in this module, established it as the anchor of the postwar international monetary system.

Why oil made it stickier

A major reinforcing factor has been what’s informally called the petrodollar system: the practice, dating to arrangements made in the 1970s, of pricing and trading the world’s oil almost entirely in US dollars, regardless of which countries are buying or selling. Because virtually every country needs to import oil, and oil has historically been priced in dollars, countries around the world have needed a steady supply of dollars just to keep their energy imports flowing - which further entrenched dollar demand well beyond direct trade with the United States itself.

A currency crisis with no US transaction in sight

Imagine a country facing a domestic economic crisis, with its own currency losing value rapidly. Much of its foreign debt, and the oil it needs to import, is priced in US dollars - so as its own currency weakens, the cost of servicing that debt and buying that oil rises sharply in local-currency terms, even though the crisis itself had nothing directly to do with the United States. This is the everyday reality of dollar dominance: a currency crisis thousands of miles from Washington can still hinge heavily on the dollar's exchange rate.

What the US gains from this arrangement

Economists sometimes describe the benefit the United States gets from issuing the world’s dominant reserve currency as an exorbitant privilege - a term coined decades ago, capturing the idea that global demand for dollars lets the US borrow more cheaply than it otherwise could, since foreign governments and investors are eager to hold US government debt as a safe, liquid reserve asset. It also gives the US considerable influence over the global financial system, since transactions routed through the dollar often pass through US banks or US-regulated financial infrastructure at some point, which is part of why US-led economic sanctions, covered elsewhere in this module, can be so far-reaching.

Whether this dominance will last

Dollar dominance isn’t guaranteed to be permanent. Some countries, wary of relying so heavily on a currency controlled by another nation’s central bank and subject to US sanctions policy, have taken steps to trade more in their own currencies or diversify reserves toward alternatives like the euro or Chinese renminbi. So far these shifts have been gradual rather than dramatic, held back by the same deep, liquid, trusted market conditions that made the dollar dominant in the first place - conditions no alternative currency currently matches at comparable scale.

Assuming reserve currency status is fixed once achieved

The British pound was once the world's dominant reserve currency before the dollar gradually displaced it across the twentieth century. Reserve currency status reflects ongoing trust and economic weight, not a permanent title - it can shift over time, even if it tends to shift slowly rather than suddenly.

Key takeaways

A reserve currency is widely held and used in global trade and savings, even by countries not directly connected to its issuer.
The dollar's dominance rests on the size, stability, and trust surrounding the US economy and its financial markets.
Oil pricing in dollars has further entrenched global demand for the currency, reaching well beyond direct US trade.
The "exorbitant privilege" of issuing the reserve currency lets the US borrow more cheaply than it otherwise could.
Reserve currency status can shift over time, as it did from the British pound to the dollar across the twentieth century.