The group - which owns Ketchum, Gavin Anderson, Brodeur Worldwide, Fleishman-Hillard and Porter Novelli International - filed the 48-page document with the US Securities and Exchange Commission following allegations of misleading the market and falsely inflating its share price.
Omnicom, led by CEO John Wren, hoped to reassure investors a week after two US law firms announced they were filing lawsuits against the group.
Berger & Montague and Kaplan Fox are filing class actions on behalf of investors who bought shares between 25 April 2000 and 11 June this year and claim Omnicom artificially pumped up its share price with misleading financial statements.
Investors taking action claim Omnicom reported revenue growth during this period, but failed to disclose up to £228m of earnout liabilities from acquisitions.
But in the SEC filing Omnicom said it had 'ample liquidity to meet all foreseeable business and capital requirements' and estimated its total earnout obligations were £254m, based on paying 30 to 70 per cent upfront for acquired firms, with the remainder in earnouts.
The group also used its analyst campaign to deny suggestions made last month about interactive arm Seneca - the subject of a Wall Street Journal article that alleged a board member had resigned over board clearance for acquisitions.