On April 26, Standard & Poor's 500 Index reduced ExxonMobil Corp.'s (NYSE: XOM) credit rating to AA+ from AAA, saying low oil prices will make it difficult for the world's largest publicly traded oil producer to keep funding high dividends and share purchases for the next few years.

The agency, a unit of McGraw Hill Financial Inc., cut Exxon's rating to AA+ from AAA, a one-notch decrease that nevertheless keeps the oil company at investment grade. S&P analysts maintained a stable outlook, implying another downgrade was not imminent.

But they noted Exxon's debt level had more than doubled in recent years due to growth projects including LNG export facilities in Papua New Guinea, as well as dividends and share repurchases, with overall spending exceeding cash flow.

Last quarter, Exxon executives said they felt it was important to be ranked at the top of the ratings scale, as the gold-plated rating was a sign of their superior business management amid the more-than 60% drop in oil prices since 2014.

"We get value from the AAA credit rating," Jeff Woodbury, Exxon's vice president of investor relations, said on a February conference call in reference to cheaper costs of capital.

Exxon's downgrade leaves drugmaker Johnson & Johnson and tech giant Microsoft Corp. as the only companies with AAA ratings from S&P 500.

The downgrade was not a complete surprise. In February, S&P 500 downgraded rival Chevron Corp. (NYSE: CVX) and warned that such a move was possible for Exxon also.

Exxon and other large oil producers have been under pressure from shareholders in recent years to boost quarterly payouts despite low oil prices. During the fourth quarter, Exxon paid out $3.6 billion in dividends and share repurchases, more than it earned.

"We believe the company may return cash to shareholders rather than building cash or reducing debt, limiting improvement in our projected credit measures when commodity prices improve," S&P 500 analysts said in a press release.

Exxon, in a statement about the downgrade, said it will focus on long-term shareholder value, regardless of oil price volatility.

"Nothing has changed in terms of the company's financial philosophy or prudent management of its balance sheet," ExxonMobil spokesman Scott Silvestri said.

The downgrade also comes as Exxon fights accusations it misled investors and the public about the risks of climate change.

Exxon is set to report quarterly results on April 29. Shares of the Irving, Texas-based company rose 0.4% to $87.65 in midday trading April 26.