SAN FRANCISCO (MarketWatch) — Shares of Kayak Software soared late Thursday after Priceline.com announced that it was buying the company, which went public in July.

Kayak US:KYAK shares were up 26% in after-hours trading, while Priceline US:PCLN was down 1.6%.

From a Prcieleine television ad Priceline

Priceline, which is based in Norwalk, Conn., announced that it was buying Kayak for $40 a share, in a deal worth $1.8 billion deal.