BOSTON -- In seven years, all taxis in the city of Boston will be hybrid vehicles, Mayor Thomas Menino said Friday.

As the city’s cabs reach their mandatory replacement age of six years, owners will be required to replace them with hybrids. Menino anticipates that within two years, 50 percent of the cabs will be hybrid vehicles.

“Requiring taxi cabs to go hybrid is an essential step in not only improving air quality, but also improving the quality of our taxi fleet,” Menino said.

Under the replacement timetable, the city expects that by 2015, 100 percent of the fleet will be hybrid.

New York and San Francisco are requiring taxis to convert to hybrids and other low-emission vehicles by 2012.

The president of the Boston's Independent Taxi Operators Association, Marckinson Charles, tells The Boston Globe his group of about 360 taxi owners isn't ready to move to hybrids. Aside from the cost, he said, drivers feel hybrids such as the Toyota Camry don't have enough trunk space.

The city estimates that a hybrid vehicle saves the average taxi driver $1,000 per year in fuel costs, while reducing emissions by 50 percent.

Boston has approximately 5,500 cab drivers and the taxis travel approximately 100,000 miles a year through the city.