It looks like the large trucks have a 4000-8000 gal capacity. <a href="http://en.wikipedia.org/wiki/Tank_truck" target="_blank">http://en.wikipedia.org/wiki/Tank_truck</a> phgi/prgl truck: <a href="http://i2.iofferphoto.com/img/1085036400/_i/3019938/1.jpg" target="_blank">http://i2.iofferphoto.com/img/1085036400/_i/3019938/1.jpg</a>