The cost of insuring Oracle's (ORCL) debt against default climbed to its highest level in nearly 18 years on Monday, while the company's bonds sold off, Bloomberg reported Monday.

Five-year credit default swaps on Oracle's debt widened to about 203 basis points, the highest level in ICE Data Services records dating back to the end of 2008, according to the report.

Bloomberg said spreads on several Oracle bonds also widened as investors assessed the company's heavy artificial intelligence spending.

Bloomberg said concerns over whether Oracle's AI investments will generate sufficient returns have intensified after S&P Global Ratings downgraded the company earlier this month to one notch above junk.