An antitrust investigation into Google's online marketing services in the US state of Texas has requested the company provide details of some of its activities.
Among the material demanded by the attorney general's office is the formula the firm uses to calculate its advertising rates.
Investigators are looking for evidence that Google is using "manual overriding or altering" of result rankings to determine if the search engine prevented competition.
Adam Kovacevich, a spokesman for the company, told Bloomberg in an email response: "While there's always going to be room for improvement, we're committed to competing fair and square," adding the company would work with the authorities to address their concerns.
Recently, when discussing an antitrust probe currently being conducted by the European Commission, chief executive officer of the firm Eric Schmidt told the Sunday Telegraph he is keen to reach a deal with investigators to avoid a long legal battle.
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