Vehicle sales in South America’s two largest markets are pulling down the region’s overall results in spite of continuous improvement in most of the smaller countries.

Deliveries fell in May for the fourth straight month in Brazil and for the third consecutive time in Argentina. This does not bode well for the rest of the year, as the two countries account for more than 80% of vehicle sales in South America.

Brazil’s deliveries slipped 9.6% in May compared with year-ago, following a 10.7% decline in April. Argentina’s tumbled 14.8% on the heels of a 7.1% drop in April, marking the largest year-on-year loss since deliveries plummeted 19.9% in September 2009.

Combined vehicle sales in the four remaining markets surveyed by WardsAuto, which have reported through April, will need to grow 57% from year-ago for the region to even match the 467,087 deliveries in like-2011.

Among the four, Chile’s April sales rebounded after three consecutive downturns. Colombia, Venezuela and Uruguay all saw gains, with Venezuela leading, up 22.5%.

Combined vehicle deliveries for the four regions in April rose 5.3% for the fifth consecutive increase. Results through the first four months were up 4.0%.

South America total vehicle sales fell 7.6% to 394,561 units in April. It was the third straight decline for the region, pushing the 4-month result down 1.3% to 1.62 million compared with year-ago’s 1.64 million.