Bermuda-based Nordic American Tanker Shipping Ltd. said yesterday it will sell 600,000 shares in addition to its previously announced offering of four million shares.

The oil tanker operator said the underwriters of the share offering had exercised in full the over-allotment granted to them by the company. The 600,000 extra shares will be sold at $30.50, the same price as the earlier four million, giving NAT total proceeds of $137 million, before expenses, from the offering.

The company intends to put the funds towards the purchase of four more vessels. NAT already operates a fleet of 15 tankers and is scheduled to take delivery of three more this year.

Morgan Stanley is acting as the book-running manager for the offering, and DnB NOR Markets is acting as co-manager.

The company expects to close the sale on January 27, 2010.