Everything in Second Life is created by its users from "primitive objects," or "prims," a set of seven fundamental shapes. Like Lego blocks, they can be combined to make useful things like nightclubs, fashion accessories, guns and cars.

Virtual vehicles are a challenge to build, said Reuben Steiger, chief executive of Millions Of Us, the company working with Scion and Pontiac to create their virtual corporate presences.

Much like extra weight in real cars, complexity slows down virtual cars and makes them drive badly. Complicated surfaces tax the virtual car's engine - the computer's processor - so little power is left to make the car drive in a quick, fluid motion.

To make a car look like something other than a rolling stack of bricks, designers must be especially creative. Basic shapes can be carved in a process sometimes referred to as "torturing the primitives." Colors can also be used as shading to suggest contours.