* Q4 net rises to C$311 mln from C$96 mln
* EPS C$0.64 vs forecast C$0.35
* Cash flow down 32 pct to C$0.46/shr
* Operating costs rise 26 pct
CALGARY, Alberta, Jan 27 (Reuters) - Fourth-quarter profit at Canadian Oil Sands Ltd COS.TO, which has the biggest stake in Syncrude Canada Ltd, more than tripled on higher oil prices and lower royalties, the company said on Thursday.
Canadian Oil Sands, which converted out of the trust format at the beginning of the year in step with federal tax changes, earned C$311 million ($314 million), or 64 Canadian cents a share, up from a year-earlier C$96 million, or 20 Canadian cents.
The company had been expected to earn 35 Canadian cents per share, the average estimate among analysts polled by Thomson Reuters I/B/E/S.
The company's cash flow, a key indicator of its ability to pay for new projects, fell 32 percent to C$222 million, or 46 Canadian cents a share, from C$328 million, or 68 Canadian cents, in the fourth quarter of 2009 as expenses rose.
Canadian Oil Sands has a 37 percent stake in Syncrude, one of Canada's largest oil sands miners and processors.
It said the its results were aided by higher revenue and a drop in royalties paid to the provincial government. As well, the company took a big charge in the fourth quarter of 2009 as it wrote off the value of Arctic gas assets.
Oil prices also improved, with the benchmark up 12 percent from the year-prior quarter to $85.24 a barrel.
During the fourth quarter, the company's share of Syncrude's production averaged 114,739 barrels per day, down 3.8 percent from the same period in 2009.
Operating costs were C$37.35 a barrel, up 26 percent.
Revenue rose 5.7 percent to C$912 million.
Canadian Oil Sands shares fell 29 Canadian cents to C$26.30 on the Toronto Stock Exchange on Thursday.
$1=$0.99 Canadian Reporting by Scott Haggett; editing by Rob Wilson