* Q4 net profit 2.29 bln riyals vs 2.13 bln riyals yr-ago
* Deposits down 2.6 pct at end of Dec. y-o-y
* Loans and advances up 0.3 pct over same period (Adds detail, context)
By Tom Arnold
DUBAI, Jan 18 (Reuters) - Saudi Arabia's National Commercial Bank (NCB) reported a 7.5 percent rise in fourth-quarter net profit on Wednesday as the kingdom's largest lender was boosted by higher income from commission and investments.
The results are the strongest in four quarters for the bank, which like other lenders in the kingdom has seen its performance clipped by weaker activity as depressed oil prices drag economic growth to its lowest level in more than three years.
The bank made a net profit of 2.29 billion riyals ($611 million) in the three months to Dec. 31, up from 2.13 billion riyals in the same period of 2015, it said in a bourse statement.
Analysts at Alistithmar Capital and SICO Capital had given forecasts for NCB's fourth-quarter net profit of 2.0 billion riyals and 2.09 billion riyals respectively.
Saudi companies issue brief earnings statements early in the reporting period before publishing more detailed results later.
Deposits at the bank, which has perhaps the closest links to the government, slipped 2.6 percent year on year to 315.6 billion riyals at the end of December, continuing the decline in levels seen in the first nine months of 2016.
The hefty deposits Saudi banks have been able to build up in recent years have diminished more recently as the government draws down cash parked with banks to help plug its budget deficit.
Loans and advances at the end of December stood at 253.6 billion riyals, up 0.3 percent on a year earlier.
The bank said total operating income rose by 3.6 percent during the quarter as a result of higher net special income, income from investments and gains on non-trading investments.
Total operating expenses increased by 0.5 percent, limited by a drop in impairment charges on financing and investments.
The bank said some year-earlier items were restated.
$1 = 3.7505 riyals Editing by Susan Fenton and Mark Potter