The three-wheeled E-Rex is an electric vehicle designed by Silicon Valley startup OptaMotive for the Progressive Automotive X-Prize. The E-Rex is being hailed as an eco vehicle three times more efficient than the beloved Toyota Prius.

The E-Rex vehicle by OptaMotive has a water-cooled permanent-magnet DC brushless motor and 96 lithium–iron phosphate cells. This allows the E-Rex to produce 45 kilowatts of energy for a range of 100 miles. E-Rex is actually an electrified version of Campagna Motors' T-Rex.