U.S. stocks lost their gains by late morning Monday as another selloff in crude oil pressured the energy sector. 

The S&P 500 was down 0.25%, the Dow Jones Industrial Average fell 0.08%, and the Nasdaq slid 0.48%.

Worries over weaker demand from China were pulling crude oil prices lower to begin the week. Analysts at Morgan Stanley forecast oil prices could drop into the $20s as the U.S. dollar strengthens against other currencies. West Texas Intermediate crude oil fell 1.8% to $32.57 a barrel, extending a decline of more than 10% last week.

The energy sector was the worst performer on markets Monday. Major oilers Exxon Mobil (XOM - Get Report) , Chevron (CVX - Get Report) , Royal Dutch Shell (RDS.A - Get Report)  and ConocoPhillips (COP - Get Report) were all lower, while the Energy Select Sector SPDR ETF (XLE - Get Report) fell 0.82%. 

China's benchmark index sank more than 5% on Monday as investors worried officials had lost control of the world's second-largest economy. The Shanghai Composite fell more than 10% last week after the People's Bank of China continued to devalue the yuan in an attempt to stabilize a weakening manufacturing sector.

"With oil futures hitting decades low levels, China devaluing the yuan and figuring out how to reduce stock market volatility, and many market participants seemingly selling the rallies instead of buying the dips, there is little optimism to be found anywhere at the moment," Schwab Center for Financial Research's Randy Frederick wrote in a note.

Stocks closed out last week with a big loss, overpowering a blockbuster jobs report The selling continued into Friday's close and sent the S&P 500 skidding 5.5% for the week, its worst start to a new year ever.

Drugmaker Shire (SHPG) climbed more than 1% after agreeing to buy Baxalta (BXLT) for $32 billion. The deal marks a 37.5% premium to Baxalta's share price in early August before news broke of a potential deal. Baxalta shares jumped 5%.

Arch Coal (ACI) filed for Chapter 11 bankruptcy as its tries to unload $4.5 billion in debt through a restructure. The company expects mining operations to continue as normal through the reorganization.

Disney's (DIS - Get Report) Star Wars: The Force Awakens continued to break new records after logging the best Saturday opening day in history in China. The film generated $33 million in its opening day and analysts expect a total gross between $200 million and $330 million by the end of its run.

Alcoa (AA - Get Report) will likely announce a $1.5 billion long-term supply contract with General Electric's aviation unit shortly, according to a report in The Wall Street Journal. The announcement could go some way to assure investors ahead of its earnings report due for release after the bell. The aluminum producer is expected to have seen a 17% drop in revenue in the last quarter.

Department store chain Kohl's (KSS - Get Report) is reportedly considering a go-private proposal, though discussions are still in the preliminary stage. The board is expected to discuss the proposal as well as the possibility of a breakup this week. Shares were up nearly 5%.

Apple (AAPL - Get Report) jumped 1% after Mizuho Securities upgraded the stock to buy. The firm said the company has "meaningful" upside potential, particularly after a recent selloff triggered by fears over weaker demand for iPhones.