Qatar became a British protectorate on 3 November 1916, when the United Kingdom signed a treaty with Sheikh Abdullah bin Jassim Al Thani to bring Qatar under its Trucial System of Administration. While Abdullah agreed not to enter into any relations with any other power without prior consent of the British government, the latter guaranteed the protection of Qatar from aggression by sea and provide its 'good offices' in the event of an attack by land – this latter undertaking was left deliberately vague. On 5 May 1935, while agreeing an oil concession with the British oil company, the Anglo-Persian Oil Company, Abdullah signed another treaty with the British government which granted Qatar protection against internal and external threats. Oil reserves were first discovered in 1939. Exploitation and development were, however, delayed by World War II.