New York ? With a plan already under way to make all of New York City’s yellow cabs green by 2012, Mayor Michael Bloomberg proposed new fuel-efficient rules on Wednesday for the thousands of black cars used by car services.

Under the proposal, the 10,000 or so black cars operating citywide would be required to meet a fuel efficiency standard of 25 miles per gallon in 2009 and 30 miles per gallon in 2010. Black cars now average 12 to 15 miles per gallon.

Black cars, which are often used by the business community, are usually summoned to a specific location, not hailed on the street, which is one of the reasons Bloomberg said it is important that they go green.

“While yellow cabs are constantly on the move, black cabs actually spend a decent amount of time just sitting and waiting for their client to come out” with their engines idling, Bloomberg said at a news conference.

Hybrid vehicles run on a combination of gasoline and electricity, emitting less exhaust and achieving higher gas mileage per gallon.

In the fleet of 13,000 yellow cabs rolling on city streets, there are now about 825 hybrids. Under Bloomberg’s hybrid yellow cab plan announced last year, that number will increase to 1,000 by October and will grow each year until 2012, when every yellow cab will be a hybrid.

By setting the fuel efficiency rule for town cars, which will go for a vote before the Taxi and Limousine Commission in April, the Bloomberg administration estimates drivers will save thousands of dollars per year in gasoline expenses.

To help defray the sizable cost of purchasing hybrid vehicles, the Bloomberg administration recruited financial institutions to chip in on a financing program.

The town cars are estimated to contribute 272,000 tons of carbon emissions each year, or 2 percent of the city’s total load of emissions from transportation sources.