According to David Closs, a professor of logistics at Michigan State, the answer is somewhere between $50 and $80 billion a year. In a story in Fortune magazine, Closs says this is the result of less efficient supply chains, higher transportation costs and more inventory. He says in the story that the average American business held 1.36 months of inventory prior to 9/11. Closs expects that figure to rise to 1.43 this year. Ten years ago it was 1.57. That means companies are giving up one-third of inventory reductions to offset the threat of terrorism.