When the tester signed up to drive a large truck, capa­ble of run­ning on either gaso­line or com­pressed nat­ural gas, he had no idea he was about to unleash a “monster”!

This heavy-duty vehi­cle with a fully loaded weight of 8,500+ pounds won’t get more than 12 to 15 mpg, but it’s pop­u­lar. What is it?

TESTED 2012 Bi-Fuel Ford F-250 Lar­iat Super Duty 4x4 Crew Cab

WHAT MAKES IT RUN? 6.2-liter V-8 (385 horse­power); 6-speed automatic.

HOW MUCH? As tested, $58,385. Base truck is $47,435; nat­ural gas con­ver­sion is an addi­tional $10,950.