Global benchmark Brent crude futures were down 13 cents, or 0.2 percent, at $74.61 a barrel by 0050 GMT, after rising 1 percent on Thursday
U.S. West Texas Intermediate (WTI) crude fell 12 cents, or 0.2 percent, to $68.07 a barrel. The contract gained 0.2 percent the previous session.
Brent is heading for a third week of gains, up around 0.7 percent, while WTI faces a small weekly decline.
“Markets continued to price in potential disruptions to world oil supplies if the United States withdraws from the 2015 Nuclear Accord with Iran,” ANZ Bank said in a note.
U.S. President Donald Trump will decide by May 12 whether to restore sanctions on Iran that were lifted after an agreement over its disputed nuclear program, which would probably result in a reduction of Iranian oil exports.
Brent has gained more than 6 percent this month on expectations the United States will renew sanctions.
Concerns about market tightness have also been fueled by the deteriorating situation in Venezuela that has led to a 40 percent decline in crude output in the country in two years.
Nonetheless, further gains have been capped by rising U.S. production as shale drillers ramp up activity in tandem with the rise in oil prices.
Surging U.S. production, which hit 10.59 million bpd last week, has encouraged record-high U.S. exports.
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