Business-development company Apollo Investment Corporation (AINV 0.74%) left no stone unturned on its most-recent conference call, providing spectacular insight into its largest oil and gas investments.

As a barrel of oil bounces between $20 and $30, investors are naturally worried about the performance of the BDC's energy-related investments. And it's for good reason -- energy investments have plagued the company's results for much of the past year.

I've summarized the detail provided in the conference call in the chart below.

Source: Conference call, quarterly report, calculations by author.

Portfolio companies Venoco, Spotted Hawk, Osage Exploration, and Miller will need restructuring, additional capital, or both. In the company's prepared remarks on its conference call, one executive said that the company believes its "marks reflect the underlying fundamentals and increased challenges faced by these four companies."

As for the remaining companies, Apollo Investment believes its stakes are "covered" by ample borrower liquidity, the value of the underlying assets, or both.

While it won't be an easy process of working through troubled credits in the oil patch, one can't find fault with transparency. Give credit where credit is due: This is perhaps the best disclosure that any BDC has offered its investors about the state of its oil and gas investments.