SEATTLE - After two years of technology investments that sent revenues and profits moving in opposite directions, Amazon.com's spending may finally be paying off.

The company's stock was up 20 percent this morning.

The Seattle-based Web retailer said its first-quarter net income more than doubled, buoyed by a lower tax rate and strong U.S. sales growth. Amazon.com also lifted its revenue outlook for the year, sending shares soaring in extended trading.

The stock climbed $5.55, or 12.4 percent, to $50.30 in after-hours trading after closing down 2 cents to $44.75 on the Nasdaq Stock Market Tuesday. In the last week, Amazon.com's shares have hovered just below their 52-week high of $45.32.

Amazon.com invested more than $1 billion in "technology and content" in 2005 and 2006 but shared few specifics about how the money was being spent. In the last year, Amazon.com launched Unbox, a movie-download service; analysts noted that the company also improved tools for third-party merchants to sell goods on its Web site and bulked up fulfillment and call centers.

Executives would not say how Unbox performed in the quarter, and they declined to comment on rumors that the company will soon launch a digital music download service. But analysts reviewing the results said the spending may finally be paying off.

Amazon.com said Tuesday after markets closed that its quarterly profit rose to $111 million, or 26 cents per share, from $51 million, or 12 cents per share, in the year-ago quarter. Results topped Wall Street's forecast for 15 cents per share, according to a Thomson Financial poll.

A $12 million reduction in Amazon's tax bite helped nudge results higher, as did a weak dollar against foreign currencies, which added about $5 million to the bottom line, the company's chief financial officer told reporters in a conference call.

Even with those caveats, the jump in profit is "proof that the investments this company made over the past two years were well worthwhile," said Scott Devitt, an analyst at Stifel Nicolaus. "This is only the beginning of the returns against those investments."

Analysts have been critical of Amazon Prime, the company's free-shipping loyalty program, and the extent to which it cuts into earnings in the past.

But that, too, may be turning around. In a conference call with analysts Tuesday, Amazon.com Chief Executive Officer Jeff Bezos said Amazon Prime helped North American sales grow faster than international sales during the quarter.

Prime is "a significant competitive advantage for Amazon," Devitt said.

During the quarter, Amazon.com said revenue rose 32 percent to $3.02 billion, surpassing Wall Street's expectation of $2.92 billion in sales.

Sales appeared strong across territories and product categories. Amazon's North America sales totaled $1.62 billion, a 30 percent jump. International sales rose 35 percent to $1.39 billion, but this figure doesn't take into account foreign exchange rates. Adjusted for currency fluctuations, the company said international sales grew 27 percent.

Amazon.com attributed overseas sales improvements in part to more third-party merchants that used the site to sell their own goods.

Worldwide, sales of books, CDs and other media products jumped 26 percent year-over-year to $1.99 billion. Sales of electronics and other merchandise rose 48 percent to $947 million.

Tom Szkutak, Amazon's CFO, said sales of so-called soft goods, which include shoes, jewelry and apparel, more than doubled in the quarter. Amazon.com launched a new shoes and accessories site, Endless.com, in January.

"I was pleasantly surprised," said David Garrity, research director at Dinosaur Securities. He said operating expenses and technology spending came in lower than what he was expecting, while the core books and music business picked up.

"They're getting some of their mojo back," Garrity said.

For the second quarter, Amazon.com said it expects revenue between $2.70 billion and $2.85 billion. The company also boosted its revenue outlook for the entire year and said it now expects from $13.4 billion to $14 billion, up from $13 billion to $13.7 billion.

Analysts are currently looking for $2.69 billion in sales for the current quarter and $13.37 billion for the year.

Amazon also said it repurchased 6 million shares for $248 million during the quarter, and its board authorized a new two-year, $500 million stock buyback program.