A. LONG DURATION WITH WIDE ACCEPTANCE
Immemorial antiquity is one of the essentials of a local custom but as far as international custom is concerned what is more important is the practice of states accepting the practice concerned as law. There are examples of short term customs that became laws i.e. customs related to sovereignty over air space and continental shelf.
B. UNIFORMITY & CONSISTENCY
In Asylum Case (1950), ICJ observed; “Rule invoked should be in accordance with a constant and uniform usage practiced by states.” Complete uniformity is not necessary but at least substantial.
C. GENERALITY OF PRACTICE
Customs generally repeated and observed by numerous states provides it base to stand as a law.
D. OPINIO JURIS et NECESSITATIS (Opinion of Law or Necessity)
When a custom is attached with the ‘opinion of law’ and its general recognition in the states becomes obligatory then we can say that the custom is international in nature.
APPLICATION OF CUSTOM AS INTERNATIONAL LAW
West Rand Central Gold Mining Co. Ltd. v. R is a case that explicitly defined the application of international custom as international law in this holding; “It should be proved by satisfactory evidence that the custom is of such nature that has received general consent of the states and no civilized state shall oppose it.”
STATE’S VIEWS REGARDING CUSTOM AS SOURCE OF INTERNATIONAL LAW
Most of the world states consider custom as an important source of international law. But there are states like Russia previously known Soviet Union which regards custom as an inadequate means for the development of international law.
INTERNATIONAL CUSTOMS WHICH GAINED STATUS OF LAW
There are many examples in this regard from the world history. One is of the communication system during wars. A messenger used to convey the message to the enemy using a horse or camel. It was custom that the envoy carrying message was not killed. Later, this custom was adopted and today we see ‘Diplomatic Envoys’ as an example of it.
Similarly, treatment with the prisoners and the quantum of force used against them, use of river water are all issues regulated by international customary law.