Pigment-based ink composition, and inkjet printing systems and methods employing such ink composition. The ink contains an aqueous polyurethane additive including polyurethane polymer chains including at least first segments having a polysiloxane group of Mw greater than about 10,000 pendant to the polyurethane polymer chain backbone, wherein (i) the polyurethane additive further comprises polyurethane polymer chains including second segments having a polysiloxane group of Mw less than about 6,000 either pendant to the polyurethane polymer backbone or a part of the polyurethane polymer backbone or (ii) the composition further comprises a polysiloxane polymer additive of Mw of less than about 6,000 which is not pendant to a polyurethane polymer backbone or a part of a polyurethane polymer backbone. The polyurethane additive has a Mw of at least 10,000 and a sufficient number of acid groups to provide an acid number greater than 20.