Abstract: A closure and sealing device for closing and sealing an open-mouthed vessel having a vessel neck and further having an orifice defined by a vessel neck lip protruding axially and radially from said orifice. A bottle cap in accordance with the preferred embodiment is designed to prevent the transfer of liquid or gas between the interior of the bottle and the atmosphere and includes two elongated, tapered sealing members disposed around the interior perimeter of the cap with the sealing members angularly disposed such that they diverge from each other. The tapered ends of the elongated sealing members are adapted to make firm contact against the top and side of the lip. Seal augmenting means consisting of a relatively massive protruding region disposed around the interior perimeter of the cap below the sealing members are adapted to urge the sealing members into sealing contact with the lip and acts as a third sealing member.