Corporate spinoffs are headed for the most active year on record as companies including Kraft Foods Inc. and AMR Corp. look for avenues to unlock value from units.

Companies announced 145 spinoffs in the first half of 2011, the most of any half-year period since Bloomberg began tracking the data more than a decade ago. At least 17 more have been disclosed since June 30. The tally, which also includes decisions by Marathon Oil Corp. and ITT Corp., exceeds the total from all of last year and is rising at an annual pace of 274, setting the stage to eclipse the record of 230 set in 2006.

"It's a revision of the corporate business model where companies would grow to balance out their businesses," said Peter Sorrentino, a senior portfolio manager at Huntington Asset Advisors in Cincinnati, which oversees $14.8 billion. "Today there's a market-implied impediment to that. And if you can't get paid for the businesses, you break them up."