* Brent hits third straight weekly rise, WTI falls this week
* Prices set for 5-6 pct monthly gain on fears over Iran sanctions
* Strong dollar, U.S. supplies hold back prices
* Speculators cut U.S. crude oil net longs -CFTC
* US drillers add 5 oil rigs this week, 28 this mth -Baker Hughes (Updates to market close, adds CFTC data, commentary)
By Stephanie Kelly
NEW YORK, April 27 (Reuters) - Oil prices edged lower on Friday, although Brent still gained for a third straight week amid supply concerns should the United States reimpose sanctions on Iran.
Brent crude futures fell 10 cents, or 0.1 percent, to settle at $74.64 a barrel. This month, the global benchmark hit highs above $75, a level last seen in late 2014.
U.S. West Texas Intermediate (WTI) crude futures fell 9 cents to settle at $68.10 a barrel, also a 0.1 percent loss.
Brent gained about 0.5 percent this week - its third consecutive weekly gain - while WTI posted a weekly loss of about 0.5 percent.
Hedge funds and other money managers cut their combined futures and options position in U.S. crude in New York and London by 17,021 contracts to 455,885 during the week to April 24, the U.S. Commodity Futures Trading Commission (CFTC).
U.S. President Donald Trump will decide by May 12 whether to reimpose sanctions on Iran that were lifted as part of an agreement with six other world powers over Tehran's nuclear program. The renewed sanctions would likely dampen Iranian oil exports, disrupting global oil supply.
"That's the biggest factor right now that's driving the market. And that's why you're seeing low volatility today and for the most part during the week," Rob Thummel, portfolio manager at energy investment manager Tortoise Capital in Leawood, Kansas.
"The market is just kind of waiting on that."
Brent has risen by around 6 percent so far this month, while WTI was on track for a gain of nearly 5 percent. The gains came despite a higher dollar, which hit its strongest since Jan. 11 against a basket of currencies.
A stronger dollar makes greenback-denominated commodities more expensive for holders of other currencies.
Concerns about market tightness have also been fueled by the deteriorating political and economic situation in Venezuela that has led to a 40 percent decline in crude output in the past two years. PRODN-VE
Price increases have been capped by rising U.S. production as shale drillers ramp up activity, underpinning a widening discount between Brent and WTI. U.S. crude's discount to Brent WTCLc1-LCOc1 hit its widest since Dec. 28 at $6.74 a barrel.
Surging U.S. production, which rose to 10.59 million barrels per day last week, has encouraged record-high U.S. exports.
U.S. drillers added five oil rigs this week, bringing the total count to 825, the highest level since March 2015, and boosted the overall rig count by 28 this month, General Electric Co's Baker Hughes energy services firm said. RIG-OL-USA-BHI
But while U.S. producers are accelerating shale drilling in areas in the United States, higher production has not necessarily translated into stronger refining results for some oil companies.
Weak refining margins hurt two of the world's largest integrated energy companies for the second consecutive quarter, although Chevron Corp's oil production gains in the first quarter outshone its larger rival Exxon Mobil Corp .
Additional reporting by Shadia Nasralla in London and Aaron Sheldrick in Tokyo; Editing by Marguerita Choy and Mark Potter