Horizontal subcontracting agreements between rival firms, each of whic
h is capable of producing and marketing its products independently, ar
e common. This article explains this practice and evaluates its welfar
e implications. The analysis shows that firms with asymmetric convex c
osts can use horizontal subcontracting to allocate production more eff
iciently between them and consequently generate a mutually beneficial
surplus. For a wide range of parameters, this increase in production e
fficiency leads to an increase in industry output. The counter-intuiti
ve result is that welfare is thereby enhanced. In fact, even when indu
stry output falls, welfare can still increase if production costs are
sufficiently lowered.