* Q3 net loss widens to 72 mln riyals from 68.9 mln riyals
* Company blames competition, difficult economy (Recasts, adds detail, context)
DUBAI, Jan 26 (Reuters) - Vodafone Qatar plans to review its costs in an effort to maintain margins, it said after reporting widening losses for a fifth straight quarter on Tuesday.
The telecoms operator has yet to make a quarterly profit, more than six years since ending state-controlled Ooredoo's monopoly in 2009.
The Vodafone affiliate had been moving steadily towards breaking even, but its performance has worsened over the past 18 months as rival Ooredoo has cut prices.
"We shall need to review our cost base further to ensure we sustain our margins," Vodafone Qatar Chairman Sheikh Dr Khalid Bin Thani al-Thani said in a statement to accompany its third-quarter results.
The business made a loss of 72 million riyals ($19.8 million) in the three months to Dec. 31, against a loss of 68.9 million riyals in the same period of the previous, according to Reuters calculations.
The result, however, was better than the 95 million riyal loss forecast by an analyst at Beltone Financial.
Quarterly revenue was 537 million riyals, down from 591.5 million riyals a year earlier, which the company blamed on difficult economic conditions and tough competition.
Average mobile revenue per user -- a key industry metric - fell to 110 riyals for the first nine months of the financial year, against 125 riyals in the same period of 2014.
Vodafone Qatar is 23 percent owned by parent Vodafone and 22 percent owned by a government-linked Qatari fund. ($1 = 3.6412 Qatar riyals) (Reporting by David French and Matt Smith; Editing by Miral Fahmy and David Goodman)