The US automobile industry is relying more heavily on fleet sales to rental companies and other commercial fleets to prop up the market, the Automotive News reported, citing research that showed that, in the first three months of 2003, new vehicles registered by fleet customers amounted to 18.6 percent of the total. In the same period the previous year, fleet customers accounted for 15.9 percent, the paper said, citing RL Polk data. Automotive News said Buick, Mitsubishi and Suzuki were especially reliant on fleet sales in the first quarter with fleets accounting for 42.6 percent of Mitsubishi sales, 38.6 pecrent at Suzuki and 36.1 percent for Buick sales. Automotive News said the Polk data highlights the brands that may be most vulnerable to weakness in the retail market and added that commercial fleets are not expected to make up the difference as they have in the past. The paper said the US rental industry, which typically accounts for half of total fleet sales, has become too weak to expand significantly, having downsized fleets as the travel industry diminished after the September 11, 2001 terrorist attacks, and did not recover.