Japanese banks, known for the risk-aversion that spared them the worst of the credit crisis, have quietly grown into some of the world's largest energy lenders.

Mitsubishi UFJ Financial Group Inc., the nation's largest bank, disclosed last month it has become one of the biggest oil and gas lenders with ¥9.2 trillion, or about $85 billion, in exposure — $45 billion more than it had reported at the end of the year.

Sumitomo Mitsui Financial Group Inc. is not far behind, with about $77 billion, and Mizuho Financial Group Inc. has about $48 billion, calculations based on the companies' websites show.