A big player in high finance is hunting for $500 million worth of forestland with the aim of harvesting carbon offsets instead of timber. Oak Hill Advisors LP, which manages $52 billion and is best known as a big debt investor, is teaming up on the venture with Bluesource, a firm that creates and sells carbon credits. The companies said they expect to buy roughly one million acres of North American woodlands and manage the properties to generate so-called forest offsets. Big companies including Microsoft Corp. and BP PLC are clamoring for offsets, which are tradable assets that represent a metric ton of carbon that has been sequestered in standing trees…. Until recently the forest-carbon business was the domain mostly of upstart companies… with air-quality regulators in California and Quebec, which operate a cap-and-trade system. [a WSJ subscription is required to access the full story]