The thermal, flow, and heating properties of unrefined fish oils (anchovy-sardine oil derived from fish processing waste, and unrefined salmon oil derived from salmon discards) blended with bunker 'A' oil (a common heating oil) were investigated. The rheological properties of the blends were examined and modeled using an Arrhenius equation approach. The onset of thermal degradation of waste fish oil, salmon oil and bunker 'A' oil were 187 degrees C, 229 degrees C and 75 degrees C respectively and complete decomposition of the oils occurred between 500 and 550 degrees C. The flow behavior index of the oil/blend samples was less than one, which indicated that the fish oil/blend exhibited non-Newtonian fluid behavior. More so, all samples showed decreasing viscosity with increasing shear rate indicated that the samples and their blends exhibited a shear-thinning non-Newtonian behavior. The average heating value of anchovy-sardine oil, unrefined salmon oil and bunker fuel oil were 38.69, 39.51 and 43.36 MJ kg(-1) respectively. The energy barrier to flow and viscosity of the blends decreased with increasing quantity of fish oils in fish-bunker mixture. (C) 2015 Elsevier Ltd. All rights reserved.