A spokesman for Navistar declined to comment on the rumors.
Navistar International stock closed at 45 1/2, up 1 3/8. Earlier in the day the stock was trading as high as 47 3/8. On December 1 when Navistar stock was trading around $38 a share, First Boston issued a strong buy recommendation saying, "Either the market, the company's management or another significant investor is bound to recognize the share value."
Speculation about a Navistar purchase by Volvo isn't new. Early this year the two sides met but were unable to come to terms on a deal.
Volvo has been flush with cash since it sold its car making operations to Ford this year for around $5.5 billion.