US car giants saw their domestic market share slump last month to 52.9%, its second lowest level ever, while Asian manufacturers notched a record 40% share.
Latest figures show that rising gasoline prices boosted sales of fuel-efficient brands (such as Toyota's Corolla, Honda's Civic and Hyundai's Sonata) by 20% or more compared with May 2005.
The Detroit-headquartered makers, still reliant on their gas-guzzling SUVs and trucks, suffered accordingly.
Sales at General Motors fell 16% last month, in part, claims the company, because it had cut back on sales to car rental companies.
GM also reported its first decline of the new version of the Chevrolet Tahoe, which dropped 5.5% compared with 2005. The company has been banking on its new SUVs and upcoming pickup truck range to bolster the turnaround plan it hopes will reverse its $10.6 billion [€8.27bn; £5.68bn] 2005 loss.
Ford Motor Company, meanwhile, has introduced a generous new incentive scheme. Its Drive On Us program will offer no-interest financing on almost all its vehicles, and give buyers a pre-paid debit card for $1,000 of gasoline purchases.
Ford had the smallest decline of the US automakers at 1.9%, benefitting from strong sales of its Focus small car and a new lineup of sedans such as the Ford Fusion, Mercury Milan and Lincoln Zephyr.
Data sourced from Financial Times online; additional content by WARC staff