Sales of Blu-ray high-definition discs exceeded sales of the rival HD-DVD format in the first half of 2007 by a margin of 2 to 1 in the United States according to Home Media Research.

Sales the Sony-backed Blu-ray discs totaled 1.6 million units from January 1 through July 1 while Microsoft-backed HD DVD sold 795,000 discs for the same period.

A combined total of 3.7 million discs have been sold since both formats first launched in the spring of 2006. Blu-ray has sold a lifetime 2.2 million discs in the US and HD DVD has sold 1.5 million discs through the end of July, according to Home Media.

In June, both Blockbuster and Target closed exclusive deals to only carry Blu-ray movies in the US.

The news bodes particularly well for Sony's PlayStation 3, which has seen a slow start since first launching in November of 2006 due to its high cost and limited number of games.