Pacific Ethanol is seeking bankruptcy protection for four of its ethanol plant subsidiaries, making it the latest maker of corn-based ethanol to face insolvency.

The Sacramento-based company has not filed for bankruptcy itself, nor is it seeking bankruptcy protection for its marketing subsidiaries, Kinergy Marketing and Pacific Ag Products.

In March, Pacific Ethanol reported that it was in default on $250 million in loans and was seeking to renegotiate terms with its creditors. It had already shut down three of its five ethanol plants and reported a $151 million loss for 2008, compared to a 2007 loss of $18.6 million.

Pacific Ethanol has held out longer than many of its competitors, however. After boom times earlier this decade, makers of corn-based ethanol have been suffering, as high prices for corn and energy have eked away at their margins and falling gasoline prices have dragged down prices for the fuel they make.

Aventine Renewable Energy declared bankruptcy last month after reporting a 2008 loss of $47.1 million, compared to a profit of $33.8 million in 2007.

And VeraSun Energy Corp. filed for bankruptcy in October (see VeraSun Files for Bankruptcy). In March, top U.S. oil refiner Valero bought out VeraSun's plants.