SPECIAL Drawing Rights, or SDRs, are often referred to as the IMF's currency. Although that is useful shorthand, the SDR is not, in fact, a currency, but rather the IMF's unit of account. The value of an SDR is defined as the value of a fixed amount of yen, dollars, pounds and euros, expressed in dollars at the current exchange rate. The composition of the basket is altered every five years to reflect changes in the importance of different currencies in the world's trading system.

SDRs nevertheless represent a potential claim on other countries' freely usable currency reserves, for which they can be exchanged voluntarily. Alternatively, countries with strong external finances can buy SDRs from countries which need hard currency. On April 2nd the G20 countries authorised the IMF to issue $250 billion in new SDRs. The advantage of a fresh SDR issuance is that it immediately augments countries' foreign reserves without needing to be lent.

However, this benefit comes with a serious drawback. Although the G20 portrayed the new SDRs as a quick way of channelling resources into emerging economies, SDRs are in fact allocated in proportion to countries' existing IMF quotas (see table).

This means that around $170 billion of the $250 billion of new SDRs that are to be issued will land in the reserves of rich countries, because they have the lion's share of existing IMF quotas. Still, the increases in the reserves of some emerging economies are not trivial. South Korea's will grow by $3.4 billion, India's by $4.8 billion, Brazil's by $3.5 billion and Russia's by $6.9 billion. Another sign of the instrument's bluntness can be seen from the fact that China's vast reserves, already nearly $2 trillion, will go up by $9.3 billion.

Of course, the IMF hopes that some rich countries (or reserve-rich emerging ones) will lend their share of the new SDR allocation to those in greater need. But this is by no means guaranteed. America, for example, needs Congress's approval to part with its share. The last proposed SDR allocation, of $21.4 billion, was approved by the IMF's board in 1997. But although 131 countries with 78% of the total votes in the IMF accepted the proposal, it was never put into effect. Such decisions require 85% support—and America, with nearly 17% of the votes in the IMF, never approved it.