In this work, it is shown that, despite the low reactivity of petroleum coke (petcoke) and the presence of 40% water, a petcoke suspension having a large colloidal population burned with unprecedented high efficiencies (>99%) without a support fuel. This paper is an account of the main combustion test results, obtained in a 6330 MJ/h pilot-scale boiler simulator located at the Babcock and Wilcox Research Center. This pilot plant simulates a full-scale utility boiler in many key aspects. Combustion tests of a typical heavy fuel oil (HFO) were carried out to produce baseline data for comparison to the colloidal petcoke in water suspension (CPW) performance. The CPW fuel showed, besides high particle reactivity during combustion, some advantageous characteristics, such as ease of pumping, metering, and atomization at room temperature, using conventional equipment designed to handle and fire HFO.