One of the most promising options to produce transportation fuels from biomass is the so-called biomass-to-liquids (BtL) route, in which biomass is converted to syngas from which high-quality Fischer-Tropsch (FT) fuels are synthesized. Pretreatment of biomass is an important part of the BtL route, both to allow feeding of the biomass into the selected entrained-flow gasifier and to reduce transport costs by densification. To determine the technological and economic potential of BtL routes, 10 integrated systems from overseas biomass to the FT product in Rotterdam are assessed on the basis of different pretreatment options, that is, chipping, pelletization, torrefaction, and pyrolysis. The main conclusions of the assessment of 10 BtL production routes are that pretreatment of the biomass at the front end of the BtL route significantly increases the economic feasibility and that overseas torrefaction is the most attractive pretreatment option. Dedicated overseas pretreatment (i.e., torrefaction and pyrolysis) is more attractive than conventional pelletization. A large-scale, central, overseas BtL synthesis plant would be the most attractive route for BtL production. However, local logistic aspects require the construction of several small-scale synthesis plants, causing significant economical disadvantages due to economy of scale. The FT product can be produced from overseas biomass for 15 euro/GJ (or 55 euro ct/L of diesel equivalent). At the crude oil prices of late 2005 (around $60/bbl), large-scale BtL can be considered as an economically feasible technology.