It estimates hybrid and diesel vehicles will account for 4.8 percent of the total US market this year.

US sales of fuel-sipping hybrid vehicles have grown rapidly over the past few years as high oil prices have cast a spotlight on fuel saving technology. The "green" vehicles are still produced in relatively small volumes, however.

"Higher gas prices are acting as a catalyst for automakers and consumers to find alternatives to the traditional gasoline internal combustion engine," Anthony Pratt, senior manager of global powertrain forecasting at the group, said in a statement.

Hybrid vehicles twin a regular gasoline engine with an electric motor and battery in which the act of braking captures lost energy, enabling vehicles to save fuel and emit fewer pollutants.

Japan's Toyota Motor Corp., which sells the popular Prius hybrid car, is a world leader in the technology along with Honda Motor Co. Ltd., which sells the Insight and hybrid versions of its Civic and Accord cars.

Detroit's Ford Motor Co. last year became the first automaker to sell a hybrid version of a sport utility vehicle, while General Motors Corp. is also aiming to introduce the technology on its bigger vehicles.

The study shows the number of hybrid vehicle models on the market is expected to increase from 10 in 2005 to 44 by 2012, while the number of diesel models is expected to grow from 14 to 26.

"The bulk of the growth in hybrid models will be in SUVs and mid-size cars," Pratt said. "The bloom of diesel vehicles will be in the pickup truck segment, as well as the luxury car and SUV segments."