* Crude pares some gains after sharp spike
* Facebook leads tech-fueled gains on Nasdaq
* Indexes up: Dow 0.8 pct, S&P 0.66 pct, Nasdaq 0.9 pct (Updates to afternoon)
By Noel Randewich
Jan 28 (Reuters) - Wall Street gained on Thursday as a blockbuster quarterly report from Facebook drove tech shares higher and a bounce in oil prices propped up the beleaguered energy sector.
Facebook surged 16.5 percent and was on track for its biggest one-day leap since 2013 after the digital advertising behemoth smashed expectations with a 52-percent jump in fourth quarter revenue.
Helped also by a 4.44-percent gain in Alphabet, set to post its quarterly results after the bell, the S&P tech sector jumped 1.6 percent.
The S&P energy sector rallied 2.6 percent, buoyed by a rise of almost 3 percent in oil prices due to speculation that Saudi Arabia and other OPEC countries would cut output to boost prices.
Optimism sparked by earnings from Facebook and a handful of other companies, as well as the bounce in oil prices, was behind most of the day's improved sentiment, investors said.
But they also warned the gains could be short-lived and that a steep selloff this year caused by weak oil and worries about China's economy may not be exhausted.
"The market was overdue for a bounce. Perhaps we're getting that now," said Chuck Carlson, chief executive officer at Horizon Investment Services in Hammond, Indiana. "I'd love to say we're onward and upward from here but I don't think things work that way."
The Dow Jones transport average, which Carlson said was a good indicator of the economy's health, was down 0.9 percent.
The Nasdaq biotech index was on track for its biggest monthly fall in 16 years and down 3.6 percent Thursday.
Abbott Labs was the biggest drag on the healthcare sector, with an 10.8-percent drop.
At 2:40 p.m., the Dow Jones industrial average was up 0.8 percent at 16,072.28 points and the S&P 500 gained 0.66 percent to 1,895.47. The Nasdaq Composite jumped 0.9 percent to 4,508.26.
Amazon, which reports after the bell, was up 7.7 percent.
PayPal, which was spun-off from eBay last year, surged 7.8 percent and Under Armour jumped 22.1 percent. Revenue at both companies beat estimates.
Among the losers, eBay sank 13.5 percent after it forecast weaker-than-expected quarterly revenue and profit.
Advancing issues outnumbered decliners on the NYSE by 2,015 to 1,008. On the Nasdaq, 1,497 issues rose and 1,235 fell.
The S&P 500 index showed eight new 52-week highs and 22 new lows, while the Nasdaq recorded 12 new highs and 145 new lows. (Additional reporting by Abhiram Nandakumar in Bengaluru; Editing by Nick Zieminski)