DBS can expect some serious questioning when it announces quarterly earnings next week. Investors may want to ask exactly how deep Singapore's biggest lender is into the oil-rig business, and just how bad the situation is for borrowers.

The bank said in an e-mail on Tuesday that it had been offering financial support to Swiber shortly before the oil-services group filed for liquidation. It said that as of end-June, Swiber had major projects with strong counterparties, and no overdue payments.

Swiber was also executing a restructuring plan that included bringing in a new investor to address its high debt levels by boosting equity, and was refinancing some of its vessels to raise cash, the bank said.