Although a modest part of the brands' overall sales, increased fleet deliveries helped offset a tough sales period. Aided by fleet sales, Hyundai scratched out a 0.7 percent sales gain in the first quarter. Nissan's total sales fell 35.2 percent during the quarter, while industrywide sales tumbled 38.4 percent.
Hyundai's fleet sales rose 29 percent for the quarter, according to Polk. Nissan's increased 21 percent.
Fleet sales include sales of vehicles to government and commercial fleets. Rental-car companies make up the lion's share of the market.
Nissan spokeswoman Julie Lawless says fleet numbers were higher than normal for the first quarter because some deliveries were delayed from 2008. But she predicts the fleet share of Nissan's sales will be higher this year than it was last year.
Chris Hosford, spokesman for Hyundai Motor America, says fleet business fell in May and will slow down to end up at 12 to 15 percent of sales.
Says Hosford: "We wanted to be sure that we took advantage of that business opportunity when some other automakers were not going to be as aggressive."
Nissan and Hyundai saw a steep drop in May total sales. Nissan sales fell 33.1 percent from a year earlier, and Hyundai declined 18.7 percent.
The Detroit 3's pullback from fleets was a conscious shift in strategy. Those makers are leaving the low-margin rental-car business rather than continuing to rely on it to keep factories running. Pushing too many vehicles into rental fleets, they concluded, hurts residual values when those cars end up at auctions.
General Motors' fleet sales fell 68 percent in the first quarter, to about 15 percent of sales, Polk data show. Chrysler LLC's fleet sales dropped 69 percent. Ford Motor Co.'s fleet sales fell about 56 percent.
Overall, the fleet market has crashed along with the U.S. retail market. For the first three months of this year, industrywide fleet sales totaled about 395,000 vehicles, down steeply from about 757,000 a year earlier, according to Polk data.