By Maria Tor and Venkatesh Iyer

Data feature produced by S&P Global Market Intelligence research groups in cooperation with the news department to highlight emerging trends and topics of interest.

The U.S. banking industry earned net income of $163.63 billion in 2015, the highest net income of any year in the SNL bank regulatory database, which dates back to 1991. The profit increase was driven by loan growth and expense reduction, offsetting a record low in interest income earned on loans. Meanwhile, the industry's provision for loan losses climbed higher in the fourth quarter.

Aggregate net income among commercial banks, savings banks and savings & loan associations in the U.S. grew by 7.5% between 2014 and 2015, after falling by 1.39% between 2013 and 2014, according to recently released bank regulatory financial data. The largest four banks, JPMorgan Chase Bank NA, Bank of America NA, Wells Fargo Bank NA and Citibank NA together earned 42.7% of the industry's income in 2015.

Though the dollar amount of net income was at an all-time high, the industry's return on average assets is still low compared to prior years. In 2015, ROAA was 1.05%, higher than 1.03% in 2014, but the industry's ROAA was greater than 1.10% in all years between 1997 and 2006.

Total loans and leases increased by $530.07 billion between Dec. 31, 2014, and Dec. 31, 2015, reaching $8.840 trillion at the end of 2015, another record high for the industry. Accordingly, banks set aside a larger amount for loan losses in the fourth quarter compared to prior quarters. The industry's aggregate provision for loan and lease losses was $12.02 billion, up from $8.50 billion in the third quarter of 2015 and $8.28 billion in the fourth quarter of 2014 .

Banks also were able to increase their profit margin earned on assets in the fourth quarter. The net interest margin, calculated as the industry's total net interest income divided by the industry's average earning assets, widened to 3.05% in the fourth quarter, compared to 3.01% in the third quarter, though it was still lower than the net interest margin of 3.06% earned in the fourth quarter of 2014. On an annual basis, the industry's NIM was 3.01% in 2015, down from 3.11% in 2014 and 3.20% in 2013.

The rate of interest income on loans and leases also hit a low in 2015, falling to 4.59% of loans for the industry, from 4.79% in 2014.

While growth in net interest income and noninterest income was lackluster, the industry was able to cut expenses, boosting profits. Net interest income in 2015 grew by 2.2% to $432.07 billion in 2015 while noninterest income grew by 2.3% to $253.23 billion. Noninterest expenses dropped by 1.27% to $417.15 billion.

At the end of the fourth quarter, nonperforming assets in the sector were down 3.1% to $165.11 billion compared to the prior quarter, and down 15.0% compared to the fourth quarter of 2014. As a percent of total assets, nonperformers came in at 1.03%, the lowest ratio since the first quarter of 2008, when it was 0.98% for the industry.

On the liability side, deposits at U.S. banks climbed to $12.19 trillion at the end of 2015, compared to $11.76 trillion at the end of 2014.

The data was compiled from aggregated financials filed in quarterly call reports. In years prior to 2012, thrift financial reports are included as well. Nondepository trusts were excluded.