Forrester, the US market research group, analyzed the debit and credit card purchases of iTunes between April 2004 and June 2006 in the US.
The company said the total amount spent on each purchase was down 17% with the average transaction costing $3 (GBP £1.50). Forrester research said that the current transaction values, hosting costs and wholesale prices were threatening to make the operation unprofitable.
Although Apple does not report iTunes sales separately, it is thought to have sold nearly 70 million iPods and 1.5 billion iTunes to date.
