An automatic downhole pump assembly comprising a housing, a sleeve slidably disposed within the housing, a piston defining an interior volume, the piston slidably disposed within the sleeve and within the housing such that a fluid pressure within the interior volume causes the sleeve to oscillate relative to the housing and causes the piston to oscillate relative to the sleeve and the housing, and a pump which is operably associated with the piston such that fluid is pumped through the pump assembly as the piston oscillates relative to the housing.