RWE AG said it sold an additional 5.2 million shares of its U.S. business, American Water Works Co. of Voorhees, for $108 million.

RWE, of Essen, Germany, said the sale, at $20.85 per share, was made to underwriters of last month's initial public offering of American Water under their right to buy extra shares. In all, 63.17 million shares have now been sold, or a 39.5 percent stake in American Water, for $1.3 billion.

Trading of the publicly held shares began on April 23 on the New York Stock Exchange at $21.50. They were up 22 cents in early-afternoon trading today at $21.25.