Jim Balsillie and Mke Lazaridis, Research In Motion Ltd.''s largest shareholders and co-chief executive officers, have lost their status as billionaires from the stock this year as it has shed more than half its value.

According to a bllomberg report, the executives, who each own about 5 percent of the BlackBerry maker, had the value of their stakes drop to about $640 million yesterday from about $1.9 billion in February.

RIM's earnings reports have disappointed investors for three consecutive quarters as the company struggles to gain ground from Apple Inc.'s iPhone and iPad. Waterloo, Ontario- based RIM missed analysts' estimates Thursday for profit and shipments of the Blackberry and PlayBook tablet computer.