Renewed interest in Wyoming's vast coal deposits began in the late 1960's as power plant demands for inexpensive, low sulfur coals increased. Because of this demand, Wyoming's coal companies have set new production records every year since 1972. Table 1 summarizes annual production for the last 19 years on a county basis. Wyoming's 1978 tonnage set yet another record at 58.2 million tons. With this tonnage, Wyoming remains the largest coal-producing state in the Rocky Mountains and the fourth largest in the nation. Coal production in Wyoming was dominated by underground mining until 1954. In that year, strip mining tonnage barely exceeded that of the underground mines. Since then, however, strip mining has become the dominant mining method and now accounts for about 99 percent of Wyoming's annual production. Conversely, underground mining has slipped to approximately one percent of the annual tonnage mined. In 1978, twenty-one coal mining companies produced 58.2 million tons of coal. These companies operated 22 strip mines and 3 underground mines.