US internet car buyers guide Edmunds.com said its price index for new vehicles decreased 0.8% from 100.2 in April to 99.4 in May due to a fall in SUV prices.

It found that this decrease was primarily the result of the significant 2.0% drop in the indices for both the large SUV and the luxury SUV segments - the third consecutive month in which SUV prices declined. Large cars experienced the largest increase, 0.9%, followed by midsize cars at 0.7%.

"Consumers are driving hard bargains on SUVs, forcing manufacturers to offer a record amount of incentives on the vehicles and pushing down the net price even further through assertive shopping," said Edmunds' data head Jane Liu.

"Neither automakers nor dealers are earning the significant profits from SUV sales to which they have been accustomed, and gas prices are to blame."

The firm's price index measures the average changes in retail prices for new vehicles with fixed options over time in order to analyse trends.