At the time, geologists relied on mapping and planing exposed rock formations, but the majority of inland Abu Dhabi was covered with sand. Due to the apparent delay in their excavations, the PDTC acquired a 75-year concession for the entire emirate. Finally, in 1951, the PDTC began drilling at Ras Sadr and Jebel Ali with holes up to 13,000 feet deep. Unfortunately, both sites revealed a dry well. After this setback, the PDTC's intention was to go to the western border of Abu Dhabi, where the presence of oil was suspected. Saudi Arabia, on the opposite border, contested this sovereignty interest because the drilling area was within a 20-mile diameter of the Buraimi oasis, a place of historical significance. Later the dispute, now known as the Buraimi dispute, was settled in favor of Saudi Arabia under the Treaty of Jeddah and closed parts of Abu Dhabi to oil.