Microexplosion of water droplets suspended in fuel oil is known to improve heat transfer and reduce the formation of particulates and NO_x. However, there exist many unsolved problems concerning the reliability of test results, the emulsion stability and the auxiliary equipment requirements. On other continents, the water/oil emulsion fuel has been tested for a number of years on various boilers, automobile engines and blast furnaces. Although claims of improved fuel economy abound, the prospect is not quite clear yet. In this review, we observe that only the colloid mills, homogenizers and ultrasonic reactors can economically emulsify the fuel oil, and propose that an effort to develop the technique in this country should give priority to collecting technical information and to well-controlled field tests with existing facilities.