Title: Numerical simulations of drop deformation for viscoelastic liquid-liquid systems. Abstract: We implement a volume-of-fluid algorithm with a parabolic re-construction of the interface for the calculation of the surface tension force (VOF-PROST). This achieves higher accuracy for drop deformation simulations in comparison with existing VOF methods based on a piecewise linear interface re-construction. The algorithm is formulated for the Giesekus constitutive law. The evolution of a drop suspended in a second liquid and undergoing simple shear is simulated. Numerical results are first checked against two cases in the literature: the small deformation theory for second-order liquids, and an Oldroyd-B extensional flow simulation. We then address the experimental data of Guido, Simeone and Greco (Deformation of a Newtonian drop in a viscoelastic matrix under steady shear flow. Experimental validation of slow flow theory. J. Non-Newtonian Fluid Mech., 114:65--82, 2003) The data deviate from existing theories as the capillary number increases, and reasons for this are explored with numerical simulations.