NEW YORK - Creditors of bankrupt Lyondell Chemical Co asked a U.S. judge to expand the investigation of the company's court-appointed examiner on Wednesday to ensure the petrochemicals company is fairly evaluating proposals from potential suitors.

Lyondell's official committee of unsecured creditors said the examiner should ensure that potential bidders like India's Reliance Industries have a chance to compete against a reorganization plan offered by a group of the company's senior creditors, which includes current owner Access Industries and the private investment firms Ares Management and Apollo Management LP.

Reliance Industries has offered up to $12 billion to acquire Lyondell, according to sources

Lyondell's unsecured creditors said in court papers they believe Reliance's offer is superior to the one proposed by Access, Ares, and Apollo.

The unsecured creditors also questioned the propriety of $440 million in adequate protection payments made to the company's senior lenders since the company filed for bankruptcy in January. They argued the exmainer should investigate why Lyondell is paying the money, which cannot be recovered.

A Lyondell spokesman was not immediately available to comment.

In October, U.S. Bankruptcy Judge Robert Gerber approved the appointment of Georgia State University law professor Jack F. Williams as an examiner and he released his report earlier this week, court documents showed.

Lyondell is among the U.S. units of LyondellBasell, which filed for bankruptcy protection, after being unable to meet its debt obligations when demand dropped for petrochemicals products during the global economic downturn.

LyondellBasell, the Luxembourg-based holding company, is owned by investor Len Blavatnik through New York-based Access Industries.

Lyondell took on billions of dollars of debt when Access Industries led a 2007 buyout of the petrochemicals company.

The unsecured creditors have argued that the deal set the company up to fail and sued the banks responsible for putting the deal together.

Lyondell recently settled that dispute, but the creditors have challenged the validity of the settlement and may ask the examiner to look into it.

The court is expected to hear the creditors' request on Jan. 12.

The case is In re: Lyondell Chemical Co., U.S. Bankruptcy Court, Southern District of New York, No. 09-10023. (Reporting by Emily Chasan, additional reporting by Chelsea Emery in New York, Santosh Nadgir in Bangalore and Pratish Naravanan in Mumbai)