This study investigates the tribological behavior of two different phosphonium-based ionic liquids as additives to a bio-oil in steel-steel contact. One of the ionic liquids is halogen-free and will be compared to an ionic liquid that contains halogens. Bio-oil and ionic liquid mixtures containing 0.5, 1 and 2.5wt. % of both ionic liquids are studied utilizing a combination of tribology and surface measurement techniques. These experiment include pin-on-disk tribometer, hydrology, corrosion, and surface spectroscopy measurements for the ionic liquid mixtures, as well as pure bio-oil for comparison. It is found that the presence of the ionic liquid additives significantly reduces the volume loss in the wear track, particularly under the higher speed studied, indicating a potentially significant improvement in function. •Lubricating ability of two Ionic Liquids was investigated as additives to a bio-oil.•Wear reductions of 68 and 74% were achieved with respect to the base bio-oil.•These results open a line to develop high performance lubricants with low toxicity.