A portable small liquefier for natural gas or coal-bed methane liquefaction has been designed and tested. The liquefier is very compact, and the compressor is directly mounted on a trailer. The liquefier is based on a mixed-refrigerant liquefaction cycle with R22 precooling. Most of the components in the liquefier are easily available off-the-shelf refrigeration products. An oil-lubricated single-stage R22 screw compressor is used for the mixed-refrigerant compression. An aluminum plate-fin heat exchanger with four flow passages was designed as the core of the cold box. The liquefier was tested for about 4 months by circulating pure methane as the natural gas resource. A maximum liquefaction capacity of 15,000 Nm(3) was achieved with a minimum specific power consumption of about 0.54 kW h/Nm(3). This liquefier can be used in various applications such as small natural gas or coalbed methane exploitations, distributed peak-shaving, and boil-off gas reliquefaction. These can also be used as a flexible distributed liquefaction center with a set of small liquefiers. (C) 2012 Elsevier Ltd. All rights reserved.