U.S. stocks waver this week amid Yellen's speech, oil prices 

U.S. stocks wavered in the week, as investors were sifting through U.S. Federal Reserve Chair Janet Yellen's comments on the country's economy as well as the volatile oil prices.

Yellen said on Monday that gradual interest rate hikes remain appropriate, but avoided providing precise timing for the central bank's next move.

"The positive economic forces have outweighed the negative, and despite the challenges that the economy continues to face, I continue to expect further progress toward our employment and inflation objectives," Yellen said in a speech at the World Affairs Council of Philadelphia.

Investors expected that a sharp decline in hiring situation may push back the central bank's decision to raise interest rates in June.

The U.S. total nonfarm payroll employment increased by 38,000 in May, well below the market consensus of 158,000 and notching the fewest monthly job gain in almost six years.

"The Fed is unlikely to raise interest rate in June or July, because it would take a doozy of a June employment rebound to unwind the weakness of March through May," said Chris Low, chief economist at FTN Financial, in a note.

U.S. stocks were well bolstered on Monday and Tuesday as the country's rate-hike expectation dims and the global oil prices increased.

Oil prices rose for a third straight day Wednesday, with U.S. oil settling above 51 U.S. dollars a barrel for the first time since July 2015, helped by a larger-than-expected U.S. crude stockpile drawdown.

U.S. crude supplies of last week lost 3.2 million barrels to 532.5 million barrels, according to the Energy Information Administration (EIA)'s weekly report released Wednesday.

Oil prices have surged over 90 percent from a multi-year low in February on a weaker U.S. dollar, a continued slide in the U.S. output and unexpected disruptions.

However, the three-day winning streak of oil prices ended Thursday as traders were looking for excuses to lock in profits. On Friday, Oil prices retreated further, with both U.S. oil and Brent crude tumbling near 3 percent, as data showed that the U.S. rig count increased for the second straight week.

The number of rigs operating in U.S. fields rose by three to 328 this week, said oilfield services company Baker Hughes Friday. Last week, the rig count rose by nine.

U.S. stocks closed both lower on Thursday and Friday, as a decline in oil prices dampened investor sentiment.

For the week, the Dow rose 0.3 percent, and the S&P 500 edged down 0.1 percent, while the Nasdaq dipped 1.0 percent. Endit