When shopping for a vehicle that will return the best gas mileage, an old maxim was that a vehicle equipped with a manual transmission -- one with a clutch that must be shifted by the driver -- would be more economical than the same vehicle using an automatic transmission.

Is that still true today? It was back when the average automatic transmission had only three gears and was a lot less efficient in transferring power to the rear wheels.

But today's automatic transmissions sort through as many as eight forward speeds under all types of driving conditions to deliver optimum performance. And the new Continuously Variable Transmissions, or CVT, use a series of belts to create, theoretically, an infinite number of gear ratios to make sure a car's power is optimized for the current road conditions.

Still, in its most basic form, a manual transmission is inherently better equipped to prove better fuel economy. The manual transmission couples the engine to the transmission with a rigid clutch instead of an automatic transmission's torque converter, which bleeds off power. The automatic transmission wastes engine power to drive the high pressure hydraulic pumps required for its operation.

But as automatic transmissions -- as well as the CVT versions -- have become more efficient and gained added gears, the fuel mileage gap between manual and automatic transmissions has narrowed, at least according to the Environmental Protection Agency.

Some examples:

enlarge [+] The Toyota Yaris, equipped with a five-speed manual transmission, is rated under the new EPA test procedure at 32 mpg in combined city-highway driving. The Yaris, equipped with a four-speed automatic transmission, is rated at 31 mpg in combined driving.   enlarge [+] The six-cylinder Ford Mustang is rated at 20 mpg when hooked to a five-speed manual transmission and 19 mpg combined with a five-speed automatic.   enlarge [+] A Chevrolet Silverado pickup with a 4.3-liter six-cylinder engine is rated at 17 mpg in combined city/highway driving with either a five-speed manual or a four-speed automatic.

For drivers in everyday situations, a manual transmission is not likely to provide any difference in fuel economy over an automatic transmission. The reason is that to achieve the optimum fuel efficiency a driver has to execute shifts at precise engine rpms (revolutions per minute). Given the challenges of city driving conditions, most drivers won't be able to realize greater fuel economy with a manual gearbox.

One consideration, however, is that usually an automatic transmission costs extra, which could factor into the buying decision. On the flip side, the majority of new vehicles aren't even offered with a manual transmission.

But when a buyer has the choice, added fuel economy of a manual gearbox will likely be outweighed by a buyer's preference for shifting gears or letting the transmission go it alone.