Stocks held at session highs by late afternoon Monday as crude oil clinched a close near $50 a barrel and as Federal Reserve Chair Janet Yellen remained vague on the central bank's rate-hike plans.

The S&P 500 was up 0.6%, the Dow Jones Industrial Average added 0.72%, and the Nasdaq rose 0.66%.

Crude oil moved higher, recapturing a level above $49, after Friday's selloff. Oil was under pressure on Friday after the number of active U.S. oil rigs showed a surprise increase in the past week. In recent months, crude has been supported by falling U.S. production which has eaten into domestic inventories.

West Texas Intermediate crude oil closed 2.2% higher at $49.69 a barrel on Monday.

Yellen, in a speech to the World Affairs Council of Philadelphia, said the U.S. is still on track for further rate hikes, though the weak May jobs report does put the economic outlook into question.

Yellen gave no time frame for further rate hikes but said that further gradual moves will "probably" be appropriate. Yellen did note that the Fed could make moves even before it reaches its growth targets

"Although the economy recently has been affected by a mix of countervailing forces, I see good reasons to expect that the positive forces supporting employment growth and higher inflation will continue to outweigh the negative ones," said Yellen.

Fed members will next meet on Tuesday, June 14, with an announcement set for the next afternoon. The chances of a rate hike in June dropped to 4% probability, according to the CME Group, after the number of U.S. jobs added to payrolls in May came in well below expectations. Chances of a rate hike in June were higher than 20% at the end of May.

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