Benchmark West Texas Intermediate crude for July delivery settled 15 cents lower at US$104.20 a barrel in electronic trading on the New York Mercantile Exchange. On Friday, the Nymex contract rose 61 cents to settle at US$104.35, bringing its weekly gain to $2.33.
Brent crude, a benchmark for international oils, was down 22 cents at US$110.32 on the ICE Futures exchange in London.
Natural gas fell after a proposed solution to a dispute over Ukrainian natural gas debts to Moscow was revealed, raising hopes that a supply cutoff would be averted.
Candy tycoon Petro Poroshenko, who supports close ties with Europe but also wants to mend relations with Russia, was leading the Ukrainian elections with about 54 per cent of the votes after 75 per cent of the precincts had been counted Monday. Former prime minister Yulia Tymoshenko was second with 13 per cent. If those results hold, Poroshenko would avoid a run-off election next month.
Oil prices have been underpinned by the threat of expanded western sanctions over Russia's role in the crisis in Ukraine, which is a key conduit for Russian gas deliveries to Europe. While Russian President Vladimir Putin said Friday his country would respect the outcome of the vote, there was still plenty of uncertainty.
Poroshenko's victory "is being interpreted as a sign of the conflict easing, prompting some market participants to take profits," said analysts at Commerzbank in Frankfurt. "All the same, it is doubtful whether the pro-Russian separatists in the renegade provinces of Donetsk and Lugansk will recognize the newly elected president."
"The ongoing lack of stability in eastern Ukraine and the continuing production outages in Libya are likely to preclude any sharper fall in prices," Commerzbank concluded.
Trading in energy futures was thinner than usual as markets are closed on Monday in the U.S. and Britain.
In other energy futures trading in New York, wholesale gasoline was down 0.5 of a cent at US$3.0183 a U.S. gallon (3.79 litres), heating oil fell 0.3 of a cent to US$2.9516 a gallon and natural gas fell 4.6 cents to US$4.374 per 1,000 cubic feet.
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