By Devika Krishna Kumar
NEW YORK (Reuters) - Oil rose slightly on Friday on futures buying, ending the week higher, but gains were limited by a strong U.S. dollar and lingering doubts about whether OPEC producers would stick to a deal to cut output.
Market players attributed choppy trading to position-squaring at the end of the week and low volumes at the start of the year.
Brent crude futures (LCOc1) settled 21 cents higher at $57.10 per barrel, after trading in a range of $56.28 to $57.47. The contract posted gains for the second week in a row.
U.S. West Texas Intermediate (WTI) crude futures (CLc1) ended the session up 23 cents at $53.99 a barrel, after swinging between $53.32 and $54.32. WTI notched its third straight weekly gain.
"There's a lot of volatility, or at least changes in direction," ABN Amro senior energy economist Hans van Cleef said. "People think the long-term trend is up, but after a gain of a few dollars, they take profit."
The dollar (.DXY) gained broadly after the U.S. non-farm payrolls report showed slower hiring in December but an increase in wages, feeding expectations of further interest rate increases from the Federal Reserve this year.
A stronger greenback makes oil more expensive for holders of other currencies.
Top crude exporter Saudi Arabia and fellow Gulf members Abu Dhabi and Kuwait showed signs they were cutting production in line with an agreement by members of the Organization of the Petroleum Exporting Countries and other producers, yet market watchers have doubts about overall compliance.
Any signs that producers are reneging on their commitments could cause sentiment to sour and cause prices to fall back sharply, Capital Economics said in a note.
U.S. energy companies this week added oil rigs for a 10th week in a row, bringing the total count up to 529, the most since December 2015, energy services firm Baker Hughes Inc (BHI.N) said on Friday.
"Market balances are unquestionably tightening, but concerns pertaining to the pace at which the global storage glut will be drawn down toward historically normal levels will be the focal point for the year ahead," said Michael Tran, director of energy strategy at RBC Capital Markets in New York.
"While the market has centered its attention on the notional size of the announced cuts from both OPEC and non-OPEC countries and whether or not the group will deliver on its promises, we believe that an important factor is being overlooked ... the deal inadvertently tightens the medium and heavy balances incrementally more than the light, sweet market."
(Additional reporting by Libby George in London, Henning Gloystein in SINGAPORE and Osamu Tsukimori in TOKYO; Editing by Susan Thomas and Richard Chang)