A buoyancy apparatus operable for connecting to a downhole tool string conveyable within a wellbore extending into a subterranean formation. The buoyancy apparatus comprises a mandrel having an axially extending bore, a first connector disposed at a first end of the mandrel and operable for connecting the buoyancy apparatus to a first portion of the downhole tool string, and a second connector disposed at a second end of the mandrel and operable for connecting the buoyancy apparatus to a second portion of the downhole tool string. A shell extends around the mandrel to define an annular space between the shell and the mandrel. A buoyant material is retained within in the annular space.