Oil alternated between gains and losses on Monday before ultimately closing lower, as optimism over an expected China-U.S. trade deal and upbeat industrial data wasn't enough to push prices higher.
During the session, Brent reached $68.99 a barrel, while WTI hit $62.34 a barrel, both the highest since Sept. 17. For the year, Brent has risen around 27% in 2019, and the U.S. benchmark is up about 36%.
"Oil prices have reached their highest level since the Saudi oilfield attack in mid-September, and thus traders are also cautious about profit-taking possibilities," she added.
Tensions in the Middle East have flared up as the United States carried out air strikes on Sunday against the Kataib Hezbollah militia group, while protesters in Iraq on Saturday briefly forced the closure of its southern Nassiriya oilfield.
U.S. officials said the air strikes were in response to the killing of a U.S. civilian contractor in a rocket attack on an Iraqi military base were successful, but warned that "additional actions" may still be taken.
Elsewhere, Libyan state oil firm NOC said it is considering the closure of its western Zawiya port and evacuating staff from the refinery due to clashes nearby.
Oil prices were also supported by declining U.S. crude stocks, which fell by 5.5 million barrels in the week to Dec. 20, far exceeding a 1.7-million-barrel drop forecast in a Reuters poll.
In China, factory activity had likely expanded again in December on stronger external demand and an infrastructure push at home although the pace of growth is set to ease as markets await more certainty on a U.S.-China trade truce, a Reuters poll showed.
China's Commerce Ministry said it is in close touch with the United States on the signing of a long-awaited trade deal.
The two countries on Dec. 13 announced a "Phase one" agreement that reduces some U.S. tariffs in exchange for what U.S. officials said would be a big jump in Chinese purchases of American farm products and other goods.