A new fuel is being developed to substitute fuel oil in power plant boilers. This fuel is a mostly colloidal suspension of petcoke in water. In this work, the flow behaviour of this fuel is evaluated by means of a rotational rheometer and a pipe viscometer. The flow characteristics of the material are complex, showing viscoelastic, and viscoplastic behaviour. There is also strong evidence of lubricated flow or slip at the wall. The results are used to obtain relevant data for engineering purposes. (C) 2014 Elsevier B.V. All rights reserved.