The Texas attorney general's office has demanded Google turn over a broad range of internal documents as part of an antitrust review of the search giant, including its formula for determining advertising rates, according to published reports.

The investigation seeks information on the company's closely guarded algorithms that run its search engine and AdWords, Google's system for displaying ads with keyword search results, according to a letter sent last July by Attorney General Greg Abbott's antitrust division and first reported today by Bloomberg News. Investigators are seeking documents related to possible "manual overriding or altering of" search result rankings, according to the report.

The investigation is also focusing on Google's shopping services sites Froogle, Google Product Search, and Google Shopping. The 13-page letter reportedly also seeks documents related to search rivals Yahoo and Microsoft, as well as complaints regarding purchasing and placement of ads on Google.

The antitrust review was revealed last September, but the scope of the investigation had been publicly disclosed until today. It is unknown whether Google has complied with the civil investigative demand--an order similar to a subpoena.

Representatives for the Texas attorney general's office did not immediately respond to requests for comment, but Google said it was cooperating with the Texas investigation.

"Since we started Google we have worked hard to do the right thing by our users and our industry, and while there's always going to be room for improvement, we're committed to competing fair and square," Google spokesperson Adam Kovacevich said in a statement. "We're continuing to work with the Texas attorney general's office to answer their questions and understand any concerns."

In February 2010, European regulators opened an investigation regarding claims by a price-comparison site called Foundem that Google was downranking Foundem in hopes of putting the site out of business. Google said last September that Texas had asked it specifically about Foundem's complaints as well as those of TradeComet and myTriggers, two U.S.-based companies that had filed their own antitrust suits against Google for allegedly manipulating search results to harm the two companies.

The details emerge as Google and the European Commission have reportedly entered into talks over resolving that investigation, and the U.S. Justice Department evaluates Google's attempted acquisition of ITA, which makes software used by the airline industry.