Western Refining Inc. (NYSE: WNR) said it had reached an agreement to buy the shares of Northern Tier Energy LP (NYSE: NTI) it did not already own, in a deal that values the refiner at $2.43 billion.

Northern Tier unitholders will now receive $15 in cash and 0.2986 of Western Refining share for each unit held, the companies said on Dec. 21.

Western Refining, which currently owns about 38% of Northern Tier, had in October offered $17.50 in cash and 0.2266 of its shares.

The revised offer values Northern Tier at $26.20 per share and represents a premium of nearly 8% to the stock's closing price on Dec. 21, according to Reuters' calculations.

The October offer had valued Northern Tier at $27.11 per share, a premium of 12% to the stock's last close.