In order to reduce ship operating costs for large oil tankers, it is effective to burn crude oil as a fuel. For this purpose, the authors have performed tests of burning many sorts of crude oil for diesel engines. The results obtained for the combustibility of crude oil with engines were good and the availability of crude oil as a fuel for diesel engines was proved. As known already, crude oil is available for boilers as a fuel. However, it has not become popular in practice on accounting the hazard of flamability by its gasified disposition. Accordingly, the authors carried out extended works for the hazard evalution in the case of using crude oil in practice and for the means of burning crude oil safely. As the results, the density of flamable gases leaked from the fuel piping was less than expectation even in the vicinity of engines. Also, it was evident that crude oil can replace residual oil as a fuel sufficiently if the proper way is taken into account