LONDON -- Major banks are contributing to the erratic behavior of a crucial global lending benchmark, a Wall Street Journal analysis shows.

The Journal analysis indicates that Citigroup Inc., WestLB, HBOS PLC, J.P. Morgan Chase & Co. and UBS AG are among the banks that have been reporting significantly lower borrowing costs for the London interbank offered rate, or Libor, than what another market measure suggests they should be. Those five banks are members of a 16-bank panel that reports rates used to calculate Libor in dollars.

That has led Libor, which is supposed to reflect the average rate at which banks lend to each other, to act as if the banking system was doing better than it was at critical junctures in the financial crisis. The reliability of Libor is crucial to consumers and businesses around the world, because the benchmark is used by lenders to set interest rates on everything from home mortgages to corporate loans.

Faced with suspicions by some bankers that their rivals have been low-balling their borrowing rates to avoid looking desperate for cash, the British Bankers' Association, which oversees Libor, is expected to report Friday on possible adjustments to the system. That report isn't expected to recommend any major changes, according to people familiar with the association's deliberations.

In order to assess the borrowing rates reported by the 16 banks, the Journal crunched numbers from another market that provides a window into the financial health of banks: the default-insurance market. Until recently, the cost of insuring against banks defaulting on their debts moved largely in tandem with Libor -- both rose when the market thought banks were in trouble.