Stock indexes were trading at all-time highs on Monday, building on the record-setting rally of the past few weeks, as oil prices jumped.
Oil hit a one-month high of about $48 on rising speculation that major producers may try to work out ways to support prices in an oversupplied market.
Strong economic data, upbeat corporate earnings and low interest rates have stoked appetite for U.S. equities, driving all three major indexes to record highs.
The S&P 500 index has notched 13 record intraday highs since July, including on Monday.
"Our sense is that we're still in this Goldilocks period where it's a sweet spot for equities and that will not change probably until the next rate hike," said Mike Bailey, director of research at FBB Capital Partners.
Investors are awaiting the minutes of the Federal Reserve's July policy meeting for more clues on when it would raise interest rates. The minutes are due at 2 p.m. ET on Wednesday.
However, traders are largely skeptical of a rate hike in the near term, with U.S. inflation below the Fed's 2 percent target and as central banks worldwide unleash stimulus programs to support their economies.
The odds of a hike stand at 12 percent for September and rise to about 38 percent for December, according to CME Group's Fedwatch tool.
Post Properties shares rose to a record high after the company agreed to be bought by Mid-America Apartment Communities for about $3.88 billion. Mid-America's shares fell 5.7 percent.
"The fact that any company would make a multi-billion dollar deal today also speaks of confidence in the U.S. market," Bailey said.
In mid-morning trading, the Dow Jones Industrial Average was up 86.7 points, or 0.47 percent, at 18,663.17.
The S&P 500 index was up 8.85 points, or 0.41 percent, at 2,192.9.
The Nasdaq Composite was up 31.09 points, or 0.59 percent, at 5,263.98.
The S&P 500 materials index jumped 1.04 percent, with all its components in the black and led by a 3 percent rise in LyondellBasell.
Apple rose 1.01 percent to $109.28 and gave the biggest boost to the S&P and the Nasdaq, while the Philadelphia SE semiconductor index touched a 16-year high.
Oil major Exxon rose 0.3 percent, while rival Chevron was up 0.7 percent.
Advancing issues outnumbered decliners on the NYSE by 2,082 to 743. On the Nasdaq, 1,913 issues rose and 746 fell.
The S&P 500 index showed 29 new 52-week highs and no new lows, while the Nasdaq recorded 110 new highs and 19 new lows.