Toyota's Prius has been a runaway success for the company. First introduced as an '01 model in 2000 in the United States market, the hybrid has continually gained in sales, gotten larger to accommodate American tastes, and has become more powerful and more fuel efficient.

According to a recent report from Motor Trend magazine, a new variant of the Prius will take boost passenger space and cargo capacity even further. Toyota is reportedly working on an "Alpha" minivan which will share its platform with the current third-generation Prius.

The Alpha is said to ride on a wheelbase that is one inch longer than the current Prius hybrid's 106.3 inches and overall length will be roughly a foot longer at around 187.6 inches. The Alpha will also have an extra row of seating bringing total passenger capacity to seven (up from five in the current Prius hatchback).

Although the Alpha will be larger and heavier than standard Prius, some of the added weight is expected to be offset by the use of a lithium-ion (li-ion) battery pack instead of the heavier nickel-metal hybrid battery pack currently used. According to Motor Trend, a li-ion pack would be roughly a third the weight of the existing battery pack.

Still, the Alpha is likely to get worse mileage than its more lithe counterpart. The Prius hatchback is rated at a combined 50 mpg, so a heftier people mover based on the same platform would probably score somewhere around 45 mpg by our estimates.

However, that would still put it ahead of small family haulers like the Mazda 5 and Kia Rondo which are rated at 24 mpg and 22 mpg combined respectively.