This report describes the development and testing of a new horizontal borehole packer for use in coal beds and evaluates commercially available packers. Gas pressure measurements and other testing procedures in horizontal holes may require as many as 30 packers in a 300-foot hole. These packers must be set simultaneously. The cost of the only commercially available packer suitable for this service is quite high, and the repair and replacement of expendable parts are quite expensive. A new hydraulic packer, which was developed, manufactured, and tested, demonstrated superiority over previously existing packers. This superiority was achieved while reducing cost about 60 percent over the best of the other packers and reducing weight almost as much. Because of a unique piston design, this new packer cannot suffer a sealing element rupture. It can be easily disassembled for maintenance in the field using inexpensive expendable parts. It is now on the commercial market, and other applications, variations, and improvements can be expected with increased usage.