Some oil-based urethanes (urethane oils) were prepared from linseed oil, glycerol, and two types of diisocyanates, hexamethyle diisocyanate (HMDI) and 4,4'-diphenylmethane diisocyanate (MDI). These urethane oils were used as a rheological modifier in solvent-based coatings. For this purpose the mixture prepared from urethane oil and alkyd resin (AR-UO) was investigated in view of flow properties. Time dependence of AR-UO was investigated by using the hysteresis loop method. None of the samples showed thixotropic flow behavior. The flow type was decided after calculation of the ratio of viscosity at low shear rate to viscosity at high shear rate. The results showed that HMDI-based samples had the smallest viscosity ratio and increasing the amount of aromatic structure caused increasing shear thinning behavior. (c) 2005 Wiley Periodicals, Inc.