Crude prices finished mixed Monday after early jumps, with Brent topping $115 a barrel before settling back for a modest gain.
Brent crude reached $115.11 (Dh422.79) a barrel in London, the highest level since early May, before settling at $113.60, up 62 cents.
New York's main contract, West Texas Intermediate crude for September delivery, ended 14 cents lower from Friday's price at $92.73 a barrel after climbing past $94 in early trade.
Japan's report that economic growth had slowed sharply in the second quarter cast a shadow over oil market demand expectations.
Gross domestic product grew a worse-than-expected 0.3 percent in the second quarter from the previous three months, the Cabinet Office said, a fourth straight rise but much slower than the brisk 1.3 percent seen in January-March.
Commerzbank analyst Carsten Fritsch tied the early gains to maintenance-forced cutbacks to North Sea production as well as tensions in the Middle East.
A collision Sunday between a US guided-missile destroyer and a Japanese-owned oil tanker near the strategic Strait of Hormuz waterway rattled nerves among investors concerned over potential supply disruptions.
Around one fifth of the world's traded oil passes through the narrow strait, which connects the oil-rich Gulf to the Indian Ocean.
Meanwhile ExxonMobil said an oil spill had been detected along the coast of southern Nigeria near its local operations, but the cause and size of the leak remained unclear.
Exxon local subsidiary Mobil Producing Nigeria confirmed that oil had been found along the shoreline of Akwa Ibom state in southern Nigeria, with residents also reporting seeing oil deposits along the coast.
A statement said the company "confirms that oiling from an unknown source has been sighted along the shoreline near Ibeno, Akwa Ibom state."