The concentration of corporate debt

Non-financial S&P 500 companies with the least cash are piling on the biggest loads of debt.

By the numbers: More than half of the S&P 500's total cash is held within just 25 companies — or the top 5% — while the bottom 95% of companies hold 73% of the index's debt, according to the Wells Fargo Investment Institute.

• The most "cash-poor" S&P 500 companies collectively have a cash-to-debt ratio of 18% — the lowest since the financial crisis. In other words, there's 18 cents of cash for every dollar of these companies' total debt.
• Alternatively, the cash-to-debt ratio at the top 25 cash-rich companies is 61%.

What to watch: Corporate debt-loads haven't hit financial crisis levels but analysts at Wells Fargo write, "leverage is rising, and debt burdens may become too large for some companies as this economic cycle extends."

Go deeper: Keep an eye on corporate debt