UPDATE 3-Valero sees 2nd quarter loss, shares down

* Sees Q2 net loss of 50 cents per share

* Shares fell 10 percent post-market

* Plans a 40 mln share offering (Adds Valero comments, paragraphs 7-9)

By Anna Driver and Erwin Seba

HOUSTON, June 2 (Reuters) - Valero Energy Corp (VLO.N), the largest U.S. refiner, said on Tuesday it would post a second- quarter loss due to weak market conditions and indefinitely delay two expansion projects.

The refiner also announced plans to issue 40 million shares to help fund its $2.5 billion capital spending plan in 2009.

The company's shares tumbled 12 percent in post-close trading.

Valero has been on a buying binge. Last month, it announced it planned to buy Dow Chemical Co's (DOW.N) stake in a Dutch refinery for $725 million. Valero also bought several of bankrupt VeraSun's ethanol plans for $477 million.

San Antonio-based Valero expects a second-quarter net loss of about 50 cents per share, far below the average forecast of analysts for a net profit of 69 cents per share, according to Reuters Estimates.