Pioneer ( PXD) completed the sale of some Gulf of Mexico assets to Marubeni for $1.3 billion in cash. The proceeds figure excludes closing costs, which are estimated to be about $140 million. The Dallas-based company expects to record an after-tax gain on the deal of $425 million to $475 million. Announced in February, the sale includes three producing projects, two potential development projects, and 87 exploration blocks. One exploration block was removed from the deal when a third party exercised a right to buy the block. The company expects to use a portion of the proceeds to buyback $359 million in shares authorized under its previously approved $1 billion share buyback program. It will also go toward reducing its short-term debt and funding part of its 2006 capital budget. Daily production from the properties being sold averaged 38,000 barrels of oil equivalent per day in December, the company said. Pioneer is retaining a 55% operating interest in Green Canyon Blocks 299 and 300, where it made a discovery in October. The company plans to develop the field and has a rig contracted to drill wells in the third quarter. The Pioneer was up 53 cents, or 1.2%, at $43.82 Wednesday.