A covenant not to sue one of the joint tort feasors, has the effect of

At common law a release of one joint tortfeasor released all of them, because there was a single cause of action. A covenant not to sue is different: it is only a promise not to sue that particular tortfeasor, so it protects him but does not extinguish the cause of action against the others (Duck v. Mayeu, 1892). Its effect is therefore to release only the tortfeasor with whom the covenant is made, while the others remain liable. It does not release all of them, and it is wrong to say that even the covenantee stays exposed, since he can rely on the covenant if sued.