SINGAPORE: Oversea-Chinese Banking Corp, Singapore's second-biggest lender, flagged worries about a weak oil and gas sector after reporting an 18% drop in quarterly profit to a three-year low, mainly due to a jump in impairment charges. Singapore banks, long lauded for their conservative lending standards, are taking a hit as companies in the oilfield services industry restructure their bonds and loans in a weak operating environment. They are also being impacted by low interest rates, shrinking their net interest margins, and a sluggish overall economy that is curbing appetite for new loans. OCBC CEO Samuel Tsien told a results briefing on Tuesday that parts of the lender's portfolio, particularly those exposed to the oil and gas services sector, would remain stressed. The sector was also a significant portion of OCBC's new non-performing loans, he said.