This disclosure is directed to a phosphate ester dispersion promoting agent and process for the preparation thereof. The present disclosure also relates to a dispersion of a particulate solid comprising the phosphate ester dispersion promoting agent and use of the phosphate ester dispersion promoting agent for dispersing a particulate solid. The phosphate ester has the structure of formula (I): in which R independently represents, at each occurrence, a polyester residue containing in its skeleton optionally at least one ether oxygen atom —O—; and x is 1, or 2.