Well, a few things.

First, it's important to know where the oil is: http://gulf2000.columbia.edu/images/maps/Oil_Persian_Gulf_Caspian_Sea_lg.png

Most of the Arabian peninsula doesn't have oil; it's concentrated almost entirely along the Persian Gulf coast in modern states like the UAE, Kuwait, Bahrain and in Saudi Arabia's Eastern Province.

From the mid-19th century until the 1970s, Bahrain, the UAE, and Oman were part of British "trucial" Oman. The Ottomans in theory controlled Kuwait, the area that is now Saudi Arabia's Eastern Province (al-Ahsa), and Qatar, but in practice it was more often a system of suzerainty over local tribal sheikhs than an actual imperial occupation.

It would nonetheless be no exaggeration to say that the Persian Gulf was a British lake from the 19th century onwards. The entire region depended on trade with India, which Britain was determined to protect and had no desire to see the Ottomans interfere with. Even in areas that were ostensibly Ottoman territory, the British often exercised control. So in Kuwait, for example, 1899 the British signed a treaty with the Emir guaranteeing his territory and control an in exchange Britain effectively controlled Kuwait's foreign policy.

The point of all this being that the major limiting factor of Ottoman in the Persian Gulf was competition from the vastly more powerful British empire.

Second, there's the issue of timing.

When WWI broke out there was some understanding of the potential value of oil as a strategic and economic resource, but it would be very wrong to say that the Ottomans "already [knew] the value of oil."

When WWI broke out, the only oil being produced in the Persian Gulf was from Iran, which was then shipped out of the Iraqi port of Basra. As an economic resource, it wasn't all that substantial. The United States was far and away the world's largest oil producer. But it had a unique strategic value because on the eve of the war the British navy had converted much of its navy from coal to oil, and the British government had agreed to purchase a controlling share in the Anglo-Persian Oil Company (which would eventually become BP.)

Securing that export route through southern Iraq is one of the reasons why the British landed at Basra literally the day after war with the Ottomans broke out.

In 1914 when the war broke out, it was thought that other parts of the region might contain oil, but no one knew where in the region it might be. Even during the war, the Ottomans were still allowing exploratory missions in Palestine, where of course there is no oil.

The most promising location at the time, even though no oil had yet been drilled there, was in what is now northern Iraq. But it's not until the very end of the conflict, in some cases actually after the armistice had been signed in 1918, that the British specifically set out to capture territory in Northern Iraq around Mosul that might have been oil bearing. Before that, it simply wasn't a major strategic objective for either side.

Oil in the Arabian peninsula wouldn't be discovered until much later. The first oil in the Arab Persian Gulf states was struck in Bahrain by the British in 1931. The first Saudi oil was struck by Standard Oil of California (today Chevron) in 1938.

Even in the 1930s there was great uncertainty about where this oil would be discovered. One of the reasons why Saudi oil was discovered by an American company is because the British didn't think there was any oil in Saudi Arabia.

Even in the 1930s however, the value of that oil wasn't necessarily all that great. It was certainly profitable for the oil companies, but the revenue that went to state coffers was just pennies on the dollar. It's not until the 1970s, the 1970 peak of American oil production, oil nationalization, and the 1973 oil embargo that the Gulf petro-dollar economy really takes off.

All of this was unknowable to the Ottomans, whose empire of course ceased to exist after WWI.