Brent crude futures were down $1.77 at $77.02 a barrel by 1330 GMT, having hit their highest since late 2014 at $80.50 this month.
Oil prices fell below $78 a barrel on Friday as OPEC and Russia considered easing supply curbs to offset disruptions in Venezuela and an expected drop in Iranian exports.
Oil prices eased as Russia hinted it may gradually increase output after withholding supplies since 2017 together with producer cartel OPEC.
Brent LCOc1 futures were down $1.08 at $79.72 a barrel by 1118 GMT, its largest one-day fall since May 8, while US crude futures CLc1 dropped 86 cents to $70.98.
Oil prices fell on expectations that OPEC members will step up production in the face of worries over supply from both Venezuela and Iran.
Brent crude LCOc1 futures were last down 53 cents at $79.04 a barrel by 1354 GMT, while US crude CLc1 slipped 24 cents to $71.96 a barrel.
Oil fell, under pressure from a potential increase in OPEC crude output to cool the market’s recent rally and cover any shortfalls in supply from Iran and Venezuela.
Oil prices edged lower with the possibility of higher OPEC output weighing on the market, although geopolitical risks are expected to keep prices near multi-year highs.
Asian shares were mostly weak with investors cautious after Trump tempered optimism over progress made so far in trade talks.
Oil rose towards $80 a barrel on Tuesday, supported by concern that falling Venezuelan crude output and a potential drop in Iranian exports could further tighten global supply.
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