Investors’ preference for the most- liquid corporate debt is running higher than any time since the credit crisis, a signal they’re preparing for the four-year rally to end.

The expense incurred by credit traders to complete bond transactions was the lowest last year relative to costs implied by the market’s average bid-ask spread since 2009, according to Barclays ($18.80 0.04%).

The shift, a sign that buyers are favoring securities that are easiest to trade, has helped financial bonds beat industrial debt by the biggest margin on record, Bank of America Merrill Lynch ($13.29 0.02%) index data show.