The two companies announced the deal, which values Kayak at $40 a share in cash and stock, late on Thursday.
Shares of Kayak surged 25.64% to $39 before market open. Priceline was off 1.89% at $616.
"Kayak has built a strong brand in online travel research and their track record of profitable growth is demonstrative of their popularity with consumers and value to advertisers," said Priceline CEO Jeffery Boyd, in a statement released after market close. "We believe we can be helpful with Kayak's plans to build a global online travel brand."Norwalk, Conn.-based Kayak also reported its fiscal third-quarter results on Thursday, posting revenue of $78.6 million, above analysts' forecast of $77.36 million. Excluding items, Kayak earned 26 cents a share. Analysts surveyed by Thomson Reuters were looking for earnings of 19 cents a share. Groupon (GRPN - Get Report) was a big loser in premarket trading on Friday, plunging 17.09% to $3.25 after badly missing third-quarter estimates. The daily deals site reported break-even earnings and sales of $568.8 million. Analysts surveyed by Thomson Reuters were looking for earnings of 3 cents a share and revenue of $590.12 million. Apple (AAPL - Get Report) shares, which lost 3.63% on Thursday, were off 0.35% to $535.86 in premarket trading on Friday. Qualcomm (QCOM - Get Report), which reported better-than-expected earnings on Wednesday, gained 0.1% to reach $60.73. --Written by James Rogers in New York. Follow @jamesjrogers >To submit a news tip, send an email to: email@example.com.