I'm referring more to the period after World War I in which the the collapse of the Ottoman Empire brought about a power vacuum in the Middle East. The region was contributing greatly to international tensions even before petroleum was discovered there. There was the struggle for influence in Iran between the British and Russians, the struggle for control of the Suez Canal and Nile River Basin between the French and British (leading to the Fashoda Incident), the German attempt to bypass Suez with the Berlin-Baghdad Railway (which led to British intervention in Kuwait). The discovery of petroleum just ramped tensions up even higher.
It seems odd that a region with such significant national security, geopolitical, and economic importance wasn't officially colonized, especially after the intense fighting that took place there during World War I. The imperial powers raced to claim small islands and marginally profitable to money losing colonies from the Central Powers, but they didn't move in to seize control of areas that were of actual strategic and economic importance?