10 things you need to know before the opening bell

Here is what you need to know.

Saudi Arabia was downgraded at Moody's. The credit rating agency lowered Saudi Arabia's credit rating one-notch to A1 from Aa3 as a result of the oil crash. Moody's says, "A combination of lower growth, higher debt levels and smaller domestic and external buffers leave the Kingdom less well positioned to weather future shocks." The credit ratings of Oman and Bahrain were also lowered by Moody's.

Goldman Sachs thinks oil's oversupply might be over. A note from a team of Goldman analysts, led by Damien Courvalin, says, "The physical rebalancing of the oil market has finally started. While supply and demand surprised to the upside commensurately in 1Q16, leaving the market oversupplied by 1.4 mb/d, we believe the market has likely shifted into deficit in May." The team cites strong demand and a sharp decline in production as reasons for the rebalancing. West Texas Intermediate crude oil is up 1.8% at $47.04 per barrel.

Warren Buffett has entered the bidding war for Yahoo. Friday evening, Reuters reported Warren Buffett is among a group of investors backing Quicken Loans founder Dan Gilbert's run at Yahoo's web assets. Verizon and a number of private equity firms are said to be involved in the bidding process. Wall Street estimates peg the value of the assets at between $4 and $8 billion.

David Tepper is out of Apple. A 13-F released by Appaloosa Management showed the fund run by billionaire David Tepper has gotten out of its massive stake in Apple. Data from Bloomberg shows the hedge fund had previously held 1.26 million shares, last valued around $133 million. The 13-F also showed Tepper maneuvered in and out of trouble pharmaceutical company Valeant, booking a profit on the trade.

Didi Chuxing has no IPO plans. On Sunday, Bloomberg reported Chinese car-hailing service Didi Chuxing, which last week received a $1 billion investment from Apple, was considering a US IPO within the next 18 months. However, a report from Tech Crunch says that's not the case. In a statement sent to Tech Crunch, Didi said, "We currently have no IPO plan, so there's no point of talking about location or schedule." Didi is in the process of raising $3 billion at a valuation of more than $26 billion.

The world's largest sovereign wealth fund is going to sue Volkswagen. Norway's sovereign wealth fund is set to sue Volkswagen over the huge losses it suffered as a result of the company's emissions scandal, AFP reports. "We have been advised by our lawyers that the company's conduct gives rise to legal claims under German law. As an investor it is our responsibility to safeguard the fund's holding in Volkswagen," Peter Johnsen, the chief executive of the fund's manager Norges Bank Investment Management, told the Financial Times. The size of the losses have not been disclosed.

Amazon is expanding its private label business. The online retailer is entering the private-label foods business. According to the Wall Street Journal, citing people familiar with the matter, Amazon will begin selling private-label brands of coffee, tea, nuts, and other items. Additionally, Amazon will offer private-label household items including diapers and laundry detergents, the people said. The offerings will reportedly be listed on Amazon by the end of the month, or in early-June.

Stock markets around the world are mixed. Hong Kong's Hang Seng (+0.8%) led the advance in Asia and Spain's IBEX (-1.2%) paces the decline in Europe. Germany's DAX is closed for Whit Monday. Here in the US, S&P 500 futures are down 0.75 points at 2042.75.

Earnings reporting is light. Agilent highlights the names reporting after markets close.

US economic data is moderate. Data for the week begins with the release of Empire Manufacturing at 8:30 a.m. ET and the NAHB Housing Market Index at 10 a.m. ET. Net long-term TIC flows will cross the wires at 4 p.m. ET. The US 10-year yield is higher by 1 basis point at 1.71%.