Google's Android mobile operating system could be running on 18 to 20 devices by the end of the year, according to Andy Rubin, Google's senior director for mobile platforms.

Speaking at the Google I/O Developer Conference in San Francisco, Rubin further said that eight or nine manufacturers would be involved in the creation of the Android-equipped phones, but reports have him declining to name which ones.

Android will continue to be open source. Manufacturers will have the option of installing Android "obligation-free" onto their devices, which means the user will have access to the OS but not Google Apps such as Gmail. A second option for manufacturers that sign a distribution agreement with Google will allow them to pre-install Google Apps onto their devices. The third option, called the "Google Experience," opens up the manufacturer's devices to Google Apps and the Android Market.

Phones that fall under the "Google Experience" will also be branded with the Google logo on the physical handset.

In April, Google rolled out the Google Android 1.5 SDK, based on the "Cupcake" branch of the Android Open Source project, and incorporating APIs for features such as home screen widgets, home screen framework, media framework and speech recognition framework.

A number of companies have announced plans to roll out Android-equipped smartphones.

HTC is currently preparing Google Android smartphones for the Chinese and Canadian markets for a June rollout. A May 26 report published in The Wall Street Journal suggested that, in China, HTC would load Android onto a version of its Magic phone that would retail for around $730. For the Canadian market, Android will reportedly be loaded onto HTC Dream and HTC Magic smartphones, via Rogers Wireless.

Analysts have previously suggested that Android, which originally rolled out in August 2008, will be running on about 12 percent of global smartphones by 2012. On top of this, Android is also being ported onto mini-notebooks, also known as "netbooks," as an operating system. With research firm IDC estimating that netbook shipments will grow from 11.4 million in 2008 to 22 million in 2009, the market represents a potentially massive growth area for Android.

In an April earnings call, Google CEO Eric Schmidt suggested that he was "excited that that investment is occurring" in Android-equipped netbooks.