Oil prices fell as traders focused on a meeting between US President Donald Trump and Ukrainian President Volodymyr Zelenskiy on Monday.
Zelenskiy is facing pressure from Washington to reach a peace deal with Russia that could involve the handover of territory.
Brent futures fell below $66 a barrel after falling 1.5% in the previous session, while West Texas Intermediate (WTI) was below $63.
Meanwhile, European leaders including European Commission President Ursula von der Leyen, French President Emmanuel Macron and NATO Secretary-General Mark Rutte are expected to attend key meetings in Washington with Trump and Zelenskiy.
Trump had previously said after his meeting with Russian President Vladimir Putin in Alaska on Friday that he would urge Zelenskiy to make a deal quickly while looking into Putin's demands that Ukraine cede large parts of its territory.
