This is one of the few methods of preservation that does not require a cure of the foodstuff before hand, so please excuse the title, continuity and all that.
There are two very traditional methods of extending the life of meats and fish by using fats. The first is the French method confit. Originally confit would be a meat, usually a waterfowl, that was first poached in it’s own fat and then stored in the same. This would be kept in jars and could last for over a year on the shelf. The second method is potting as in Morecambe Bay potted shrimps. The food is first cooked and then covered in melted, clarified butter. This seals in the shrimps and again drastically extends shelf life.
A more modern method of preservation is to keep food in oil. This can be to either preserve the food such as in canned tuna or to flavour the oil. Both of the techniques leave a flavoursome oil but neither are without their dangers. Oil does not necessarily carry any toxins but it can help anaerobic organisms thrive on other foods. A pathogen like botulism can be carried on garlic that has not been prepared properly. Basic food hygiene eliminates such risks, so keep it clean and happy preserving.