The city's fleet of yellow cabs will go entirely hybrid within five years, and all new vehicles for hire will have to meet new emissions and mileage standards by next year, Mayor Michael Bloomberg is set to announce Tuesday.

Today, there are just 375 fuel-efficient hybrid vehicles among the 13,000 taxis rolling on city streets. That number will increase to 1,000 by October 2008 and will grow by about 20% each year until 2012, when every yellow cab will be a hybrid.

Hybrid vehicles run on a combination of gasoline and electricity, emitting less exhaust and achieving higher gas mileage per gallon. Changing over the fleet is part of Bloomberg's wider sustainability plan for the city, which includes the goal of a 30% reduction in carbon emissions by 2030.

The hybrids that have been successfully tested in the city's taxi fleet over the past 18 months include the Toyota Motor Corp.'s ™Prius, the Toyota Highlander Hybrid, the Lexus RX 400h, Ford Motor Co.'s (F) Escape.

Bloomberg was to discuss the hybrid changeover on NBC's "Today" show, on which Yahoo! was expected to announce a donation of 10 hybrid Ford Escape taxis, which get 36 miles per gallon. The details were described to The Associated Press before the mayor's appearance.

The standard yellow cab vehicle is the Ford Crown Victoria, which gets 14 miles per gallon.

Besides making the yellow cab brigade entirely green within five years, the city will require all new vehicles entering the fleet after October 2008 to achieve a minimum of 25 miles per gallon. A year later, all new vehicles must get 30 miles per gallon and be hybrid.

City officials said the new standards, when fully implemented, are expected to reduce carbon emissions by more than 200,000 tons per year.

Hybrid vehicles are typically more expensive, but the city said the increase in fuel efficiency will save taxi operators more than $10,000 per year.