An injectable bone mineral substitute material composition comprises an inorganic bone cement powder and a biologically compatible oil. The oil is an intermixture with the cement powder at a concentration of less than 10 wt % of the total weight of the composition in order to improve the rheology of the same. In a method of intermixing a powder of an implant material and a biologically compatible oil to a composition the oil is mixed with the powder of implant material at an elevated temperature.