NEW YORK — Rumors of a possible merger between Yellow Corp. and Consolidated Freightways Corp. prompted heavy trading in both company’s stocks yesterday.

Such a merger would combine two of the largest trucking operations in the United States and create the second-largest trucking company in the world behind United Parcel Service.

Neither company could be reached for comment.

CF saw its stock close Tuesday at 16 116, up 1/8 on Tuesday, on volume of 1.5 million shares (average daily volume in the stock is generally 125,000 shares). It hit a high of 18 3/8 at midday. Yellow Corp., the nation’s largest publicly traded trucking company, saw its stock up 1 point to close at 17 1/4 on volume of 210,900 shares (average daily volume: 133,000 shares).

Both stocks trade on the Nasdaq exchange.

CF and Yellow both specialize in less-than-truckload freight. Investors are apparently hoping that a merger would create savings and value through rationalization in infrastructure and employees, making them better able to compete with non-union carriers. CF started trading separately two years ago after a spinoff from what is now CNF Transportation Inc.

Yellow employs 29,000 people; CF 22,000. Hourly workers at both companies are represented by the Teamsters.

Yellow Corp. operates Yellow Freight System Inc., the second-largest LTL carrier in the U.S. after Roadway Express Inc. It also owns several regional, non-union LTL carriers. Yellow Corp. lost $37 million during the first nine months of this year, primarily due to the cost of selling its Preston Trucking Co. subsidiary. Net income from other operations was $29.6 million. Revenue was $2.2 billion, and its operating ratio on continuing operations was 97.2%, up from 96.3% in the year-earlier period.

CF is the third-largest LTL carrier in the U.S. Net income was $23.7 million in the first nine months of the year, up 8% over the same period the year before. Its operating ratio was 97.1%, unchanged from the year-earlier period.

CF is comprised of CF MotorFreight of Menlo, Calif.; Calgary-based Canadian Freightways; LTL hauler Epic Express, which served Ontario and Quebec; Canadian Sufferance Warehouses; and customs broker Milne & Craighead.