Deep eutectic solvents (DES) are novel liquids composed of inexpensive components, and are non-flammable, with a low volatility. One problem with DES is frequently their relatively high viscosity so selecting components which make a tractable liquid with low enough melting point and viscosity to be useful in applications is challenging. Here we wish to probe the structure of DES which have similar components but very different viscosities & melting points, based on tartaric acid (TA) with either choline chloride or urea, both frequently used in DES formulation. TA-based DES also allow us to study the role of chiral components on DES structure, since the D- and L- forms are both readily availably, and can be mixed to make a racemate. We will compare the structures of choline chloride:TA, urea:TA, and related urea:potassium sodium tartrate which span a range of viscosities & melting points