In this study equations have been set up allowing the calculation of the viscosity depending on temperature and total solid content of the algal sample and the shear rate. Therefore, the viscosity of the marine microalgae Nannochloropsis salina was determined experimentally at different temperatures and TS contents. Untreated, thermal pretreated and digested algal biomasses were investigated. For all samples a non-Newtonian and shear-thinning behavior was detected indicating pseudoplastic fluids. The viscosity of all samples increased with increasing TS content and decreased with increasing temperature. For the analyzed samples the resulting relative deviations between experimental and calculated viscosities were mainly within a range of +/- 4.0%. (C) 2014 Elsevier Ltd. All rights reserved.