* Q4 net profit 815 mln riyals vs 655 mln riyals yr-ago - statement
* Beats average estimate of analysts
* 2012 net profit 3.24 bln riyals vs 2.89 bln riyals in 2011 (Adds detail)
DUBAI, Jan 14 Saudi British Bank (SABB) posted a bigger than expected 24.4 percent rise in fourth-quarter net profit, with its loans portfolio, customer deposits and earnings from special commissions all rising over the year.
Saudi Arabia's fourth-largest listed bank said in a bourse filing on Monday it made 815 million riyals ($217.3 million) in the last three months of 2012 compared to 655 million in the last quarter of 2011. It cited higher operating income and a decrease in operating expenses for the rise.
Total operating income in Q4 was 1.23 billion riyals, an improvement of 9.5 percent over the same period of 2011.
Nine analysts surveyed by Reuters had forecast it would earn a net profit of 771.7 million riyals.
Net profit for all of 2012 was 3.24 billion riyals, up 12.2 percent on 2011's 2.89 billion riyals.
Fourth quarter profit from special commissions, at 821 million riyals, grew 12.4 percent over the same three months of 2011. Full-year figures were up 8 percent over the previous year.
SABB's loans portfolio climbed 13.3 percent over the course of 2012 to 96.1 billion riyals at the end of the year.
Customer deposits at the end of 2012 stood at 120.4 billion riyals, up 14.1 percent on the same point of 2011, while total assets increased 13 percent over the course of 2012 to 156.7 billion riyals.
Saudi banks have enjoyed successive years of expansionary government budgets, ample liquidity and improving corporate loan demand. ($1 = 3.7505 Saudi riyals) (Reporting by David French; Editing by William Maclean and Hans-Juergen Peters)