Unocal Corp. on Monday agreed to sell its Canadian oil and gas exploration and production portfolio to Pogo Producing Co. for $1.8 billion in cash, the companies said in statements.

El Segundo-based Unocal intends to sell all of the stock in its Canadian subsidiary Northrock Resources Ltd. to Pogo and said it would realize about $1.5 billion in after-tax proceeds. Northrock, which represents essentially all of Unocal’s Canadian oil and gas reserves and production, accounted for less than 7 percent of its global reserves at the end of 2004 and its production as of the first quarter.

Houston-based Pogo, which explores for and develops oil and gas assets in the Gulf of Mexico and New Zealand, said the deal would boost proven oil and gas reserves by 45 percent, increase its net acreage by about 82 percent, add more than 900 drilling opportunities, and extend its reserve life to 9.3 years. The deal will help Pogo save about $5 million a year in administrative and operating costs.

Pogo plans to buy Northrock with cash, proceeds from asset sales, capacity under an existing revolving credit line, and transactions in the capital markets. The company said it expected to reduce acquisition-related debt in 2006 and 2007.

The deal is expected to close in the third quarter, pending Canadian approvals. The deal is unrelated to Unocal’s pending acquisition by Chevron Corp., which will be voted on by shareholders on Aug. 10.

Northrock represents Pogo’s first large acquisition since its purchase of North Central Oil Corp. in 2001.

In addition, Pogo said Monday it will maintain its share repurchase program, under which it has already bought back $220 million worth of shares. The company’s board authorized the repurchase of at least $275 million of Pogo’s common stock, with a ceiling of $375 million.

Unocal shares rose 0.4 percent to settle at $65.97 on Monday.