Systems and method for sealing vascular penetrations rely on placement of a temporary barrier on the posterior side of the penetration. Penetrations are then sealed by delivering a hemostatic gel to a region over the penetration, where the barrier both inhibits loss of the gel and promotes back flow of blood into the gel. A combination of natural clotting factors in the blood and hemostatic agents in the gel promote rapid and effective sealing of the vascular penetration. Specific systems for performing the method include a barrier carrier for temporary placement of the barrier within the blood vessel and a gel delivery tube which may be positioned within a tissue tract or line of penetration simultaneously with the barrier carrier to deliver the hemostatic gel.