Group 1, which has BMW dealerships in southern England, is understood to be in the final stages of adding Audi to its portfolio.
A source outside the company told AM that general managers have been informed of the sale to Group 1 by their employer, Hodgson Automotive, which trades as Essex Audi and has seven dealerships with the German premium brand.
US-based Group 1, which began sales in the UK in 2007 with its takeover of Chandlers BMW and expanded by buying Barons BMW in 2010, said earlier this year it wanted to expand.
Its president Earl Hesterberg has told AM: "Fifty dealerships is a nice sized business."
AM is awaiting a response from Hodgson Automotive owner Kevin Walter.