SEATTLE — Amazon.com Inc.'s second-quarter profit more than tripled, boosted by strong sales of books, music and electronics worldwide. The Web retailer's stock soared 11.3 percent in after-hours trading.

Earnings for the three months ended June 30 climbed to $78 million, or 19 cents per share, from $22 million, or 5 cents per share during the same period last year, the company said Tuesday.

Results topped Wall Street's expectations. Analysts surveyed by Thomson Financial forecast a profit of 16 cents per share.

Revenue rose 35 percent to $2.88 billion from $2.14 billion in the year-ago quarter, beating analysts' expectations for $2.81 billion in sales.

Prior to the announcement, shares of Amazon sank $2.49, or 3.5 percent, to close at $69.25. They gained $8.72 to $77.07, in after-hours trading.

Sales in the U.S. and Canada rose 38 percent to $1.6 billion. In the company's U.K., German, Japanese, French and Chinese sites, revenue increased 31 percent to $1.28 billion. Amazon said a weaker dollar helped improve sales slightly.

Worldwide, sales of books, music and other media-category products grew 27 percent to $1.83 billion. Revenue from electronics and general merchandise improved 55 percent to $970 million.

In a conference call, Chief Financial Officer Tom Szkutak said items sold by third-party merchants increased to 30 percent of total unit sales on the site, up slightly from a year ago.

Amazon's spending to help third parties sell items on its site, storage and computing power for software programmers and other items rose 10 percent to $201 million, but slowed considerably from the year-ago quarter.

The retailer also said the number of subscribers to its $79-per-year unlimited shipping membership program increased, but did not disclose a total. Free shipping eats into Amazon's results, and the company said net shipping costs totaled $75 million.

For the current third quarter, Amazon said it expects revenue from $3 billion to $3.18 billion. For the full fiscal year, Amazon raised its forecast to $13.80 billion to $14.30 billion, up from its earlier outlook for $13.4 billion to $14 billion.

Wall Street is currently looking for third-quarter revenue to reach $3 billion, and for full-year sales of $13.84 billion.