The Google Nexus 7 heightens competition in the red-hot market for tablet computers, which is dominated by the Apple iPad but has a number of other players.

An ABI Research survey showed overall global sales of media tablets amounted to 18.2 million in the first three months of the year, up 185 percent from a year earlier, but down 33 percent from the fourth quarter gift-giving season.

Here are some of the major entries in the tablet industry, with prices for US consumers:

APPLE IPAD

Apple held 65 percent of the market in the first quarter with 11.8 million iPad shipments, boosted by the launch of a third-generation model and price reductions on the iPad 2, according to ABI.

The newest version launched in March sold three million over the course of its first weekend on the market. It features a screen of 9.7 inches (24.6 centimeters) and still and video cameras.

The new iPad sells for $499 and up depending on memory size and whether a buyer chooses Wi-Fi or 3G connectivity. The iPad is also backed by Apple's online entertainment store iTunes and more than 500,000 free and paid applications in the App Store.

GOOGLE NEXUS 7

The newest entrant to the field, Nexus 7 is smaller than the iPad at seven inches, and much cheaper at $199. It roughly matches the price and dimensions of Amazon's Kindle Fire. Nexus weighs 340 grams (12 ounces), runs the latest version of the Google Android operating system, and links to Google Play, the tech giant's answer to iTunes and Amazon for books, films and other content. It is to be available starting in mid-July.

MICROSOFT SURFACE

Microsoft said this month it would launch a new Windows-powered tablet with a cover that, when opened, acts as a keypad that switches into "desktop" mode. Pricing was not announced, but some reports say it could be more expensive than the iPad, starting at $599.

It boasts a 10.6-inch (26.9 centimeter) high-definition screen and will be available with 32 or 64 gigabytes of memory. A model powered by Windows 8 Pro weighs 903 grams (two pounds) and will be available with 64 or 128 gigabytes of memory.

Surface appears to straddle the tablet and the "ultrabook" PC market, and will have access to some 100,000 apps for Windows users.

SAMSUNG GALAXY

Samsung has overtaken Amazon as the number two tablet seller, and up to now the largest maker of Android-powered devices. The South Korean firm shipped 1.1 million tablets, or six percent of the global market, overtaking Amazon, which saw an 80 percent quarter-over-quarter drop in sales of the Kindle Fire, according to ABI. The 10-inch Samsung Galaxy Tab sells for $400, but this week a judge ordered sales halted, saying it infringes on patented designs of the iPad. Samsung also sells a smaller tablet at $249, similar in size to Nexus 7 and Kindle Fire.

AMAZON KINDLE FIRE

The Kindle Fire introduced last year grabbed a significant chunk of the market, helped by its $199 price tag at the start of the holiday season. Amazon does not release Kindle sales figures, but research firms say the Fire has lost steam since its launch. IDC reported Kindle Fire had just four percent of the market in early 2012, compared with 16.8 percent in the fourth quarter.

Kindle Fire features a seven-inch (17.78-cm) screen and has a modified version of Google's Android software. It does not have a camera or 3G connectivity, only Wi-Fi. It comes with a pre-installed shopping application as Amazon seeks to drive Kindle Fire buyers to its online store, which features books, music, movies, TV shows and games.

OTHERS

The BlackBerry PlayBook from Canada's Research In Motion made its debut last year to desultory reviews and sales have been sluggish. Priced initially between $499 and $699, RIM has been cutting the price since then in a bid to spur demand.

The Nook tablet from bookseller Barnes & Noble at $249 offers an alternative to Kindle Fire, serving as an e-reader with access to the store's e-books and other content, and a modified Android system for Web access.

PC makers including Lenovo and Asus have also been selling tablets. Other vendors including Dell, Hewlett-Packard and LG are currently retooling tablet portfolios for mid-year launches, using Android or the Windows 8 platform.