Sterilizing apparatus and method for dental and surgical tools. A main sterilizing chamber is provided with a cover having heating means and capsule-supporting means, which may comprise a plurality of removable trays, each one of which has a capsule-supporting basket. A plurality of tool-holding capsules are removably mounted in the capsule-supporting means and a normally solid petroleum product that is liquid at sterilizing temperatures surrounds and covers the capsules. The same kind of material is within each capsule in contact with the tool. The capsules are hermetically sealed by removable closures, and they include a tool-support structure inside. The tools are placed in the capsules and the capsules into the container, usually by means of the trays and basket, and then the sterilizer is heated for the necessary time at the necessary temperature to obtain sterilization, the heat acting through the medium of the normally solid petroleum product. After sterilization is completed, the baskets may be removed and drained, and the capsules may be stored. The petroleum product eventually solidifies and retains the product in sterile condition inside the sealed capsules.