Successful feeding is critical to biomass utilization processes such as gasification and combustion, but feeding is difficult due to the adverse effects of heterogeneity, physical characteristics and moisture content of the particles. The objectives of the present study were to define blockage mechanisms and plug seal with the aid of tapered and extended sections. Wood pellets, sawdust, hog fuel and wood shavings were delivered by a screw feeder/lock hopper system. The experimental results showed that tapered and extended sections increased torque requirements significantly while improving the plug seal to the reactor, with performance depending on biomass physical properties and screw feeder characteristics. (c) 2007 Elsevier B.V. All rights reserved.