Groupon used non-standard accounting in its S-1 public offering filing, but following regulatory pressure it will amend its documents to eliminate that element, according to an exclusive report in AllThingsD.

The Chicago-based company reported its revenue and profits using ACSOI – adjusted consolidated segment operating income. The Securities and Exchange Commission and most investors prefer S-1 filings that conform to the principles of GAAP (generally accepted accounting principles).

In the first quarter of 2011, Groupon reported its revenues and profits using Adjusted CSOI as $81.6 million. Calculated on a GAAP basis, the company lost $113.9 million.

Crucially, Groupon’s Adjusted CSOI does not include marketing costs and costs related to acquisitions. All ThingsD reported the company spent $263.2 million in marketing during 2010, “an astronomical leap over the $4.5 million it reported for 2009,” and spent $203.2 million on 13 acquisitions.

“We spend a lot of money acquiring new subscribers because we can measure the return and believe in the long-term value of the marketplace we’re creating,” Andrew D. Mason, the company’s co-founder and chief executive, wrote in a letter to potential shareholders.

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