Abstract: A reciprocating gas horizontal compressor with free lifting piston, which includes a piston with straight ends and inclined compression chambers, a crankcase in which are mounted a crankshaft, a connecting rod fixed to a cross head thru a bolt which alternately drives in a cross-head body a piston rod, and a cylinder body which contains a cylinder liner in which is moving rectilinear and alternatively an improved piston provided with straight ends and compression chambers inclined in areas (m) and (k), with the same angle and in the same plane as a zone (p) from a first cylinder head element and respectively in a zone (n) from a second cylinder head element, and some magnets fixed to the piston and some magnets fixed outside and to a lower part of the cylinder liner, through which the piston is free lifting on the stroke length with reduced friction.