Thai Life Insurance may sell a stake of at least 20 percent, sources familiar with the matter said, in a deal that could value the country's No. 2 life insurer at about $2.5 billion and mark the third auction in the domestic sector within a year amid a huge wave of Thai M&A. Highlighting fast-growing interest in one of Asia's most underdeveloped insurance markets, the potential sale comes on the heels of Prudential $590 million acquisition of Thanachart Life Assurance in November and Hong Kong tycoon Richard Li's purchase of ING's Hong Kong and Thailand units for $2.1 billion in October.