The S&P 500 rose 7 points, or 0.5 percent, to 1,347 in midday trading. The Dow Jones industrial average rose 59 points, or 0.5 percent, to 12,697. The Nasdaq composite index rose 18 points, or 0.6 percent, to 2,845.
Marathon Oil Corp. rose 4.4 percent, one of several energy producers to benefit from a 4 percent jump in crude oil. It is once again above $101 per barrel. Baker Hughes Inc., which helps companies drill for oil and gas, gained 4 percent. Energy companies within the S&P 500 rose 1.5 percent, the most among the 10 industries in the index.
Freeport McMoRan Copper & Gold Inc. rose 1.9 percent after copper rose 1.6 percent and silver rose 6.1 percent. Producers of metals and other materials rose 1.1 percent, second best among the S&P 500 industries. Metals and other commodities recovered some of their steep losses from last week, when silver tumbled 27 percent and oil sank 15 percent.
The nation's largest food distributor, Sysco Corp., jumped 12.1 percent after reporting a 4 percent rise in income. Analysts had expected a drop.
Dollar Thrifty Automotive Group Inc. rose 12.9 percent after Hertz Global Holdings Inc. raised its buyout offer for the car rental company to more than $2.2 billion. Rival Avis Budget Group Inc. is also trying to buy Dollar Thrifty.
McDonald's Corp. rose 1.3 percent after reporting that its global sales rose last month. The strongest growth came from its restaurants abroad, which stretch from Europe to the Middle East to Asia.
Tyson Foods Inc. sank 5.8 percent after reporting that its earnings were flat from a year ago.
Most companies in the S&P 500 have reported earnings for the first quarter, and the trends have been strong. Through Friday, nearly three out of four companies released earnings that beat analysts' expectations.
Economic data, by contrast, has been mixed. Growth for the manufacturing industry slowed last month, and the economy grew at a lower-than-expected 1.8 percent in the first quarter.
European stock markets fell on worries that Greece will need more help managing its debt. Standard & Poor's downgraded Greece's debt rating even further into junk status. France's CAC 40 index dropped 1.3 percent, Germany's DAX index sank 1.1 percent and Britain's FTSE 100 fell 0.6 percent.
The yield on the 10-year Treasury note was flat at 3.15 percent. The yield remains close to its lowest point of the year, 3.13 percent. It fell that low on Friday after a German magazine claimed that Greece may drop the euro currency. Greece's government strongly denied the claim. Worried investors have bought Treasurys, traditionally seen as a safe investment. When Treasury prices rise, their yields fall.