Back in black! Dow, Nasdaq, S&P 500 up for '15

The start to the year for stocks was a downer, but a February renaissance for stocks continued Thursday as all three major benchmark indexes shot back into positive territory for the year.
The Dow Jones industrial average was higher for a fourth straight session as it jumped 211.86 points, or 1.2%, to 17,884.88. It was the best 4-day streak for the blue chip index since Dec. 17-22, 2014.
The Standard & Poor's 500 index gained 21.01 points, or 1%, to 2062.52 and the Nasdaq composite rose 48.39 points, or 1%, to 4765.10.
The advance Thursday has been broad-based, with all 10 sectors in the S&P 500 sporting gains .
Oil prices on the U.S. market -- hammered over the past several months and volatile of late -- jumped Thursday as benchmark U.S. crude moved back above $50 a barrel. The contract was up 4% in electronic trading on the New York Mercantile Exchange to $50.48 a barrel.
In corporate news:
• Investors who owned shares of Hospira woke up much richer Thursday after Pfizer bought the injectable drugmaker for $90 a share, a premium of nearly 40% from Wednesday night's close.
Hospira shares (HSP) surged 35% to $87.64 and Pfizer (PFE) gained 2.9% to $32.99.
• Sprint (S) reported a loss during its third quarter, but the wireless carrier said it added nearly 1 million new customers during its third quarter. That sent the stock up 5% to $4.82.
Meanwhile, the U.S. trade deficit widened substantially to its highest level in more than two years in December as the strong dollar hurt exports and bolstered imports.
The trade gap jumped $6.8 billion, or 17%, to $46.6 billion, highest since November 2012. Economists expected a decline to $38 billion.
Global stock markets were volatile as the European standoff over Greece's bailout intensified.
Greek shares plummeted Thursday after the European Central Bank said it would stop offering government-backed credit to banks there. The volatile Athens stock exchange fell as much as 10% before recovering slightly to end down 3.3%. Greece's new government is insisting it will stick to its anti-austerity agenda.
Other European markets pared early steep losses and closed mixed. Germany's DAX ended down only 0.1% at 10,905.41 after a volatile session spent mostly in the red. Britain's FTSE 100 ended up 0.1%to 6865.93 at the end of slow climb out of negative territory. France's CAC 40 gained 0.2% to 4703.30.
In Asia, Japan's Nikkei 225 index dipped 1% to 17,504.62 and Hong Kong's Hang Seng index gained 0.4%. The Shanghai Composite dropped 1.2%.
Stocks closed mixed in volatile trading Wednesday as oil prices broke a four-day rally and plunged almost 9% on a jump in crude supplies. The Dow closed up 0.04% and the S&P 500 dropped 0.4%.
Contributing: Associated Press