St. Louis – February 3, 2000 - Arch Coal, Inc. (NYSE:ACI) announced today that it has temporarily idled its West Elk underground mine in Gunnison County, Colorado, following the detection of higher-than-normal levels of carbon monoxide in a portion of the mine. Following the detection of these elevated levels around mid-day on Friday, January 28, the company immediately evacuated the mine and launched an investigation to determine the cause of these unusual readings.

"Since Friday when we detected the problem, gas levels in that portion of the mine have diminished but remain moderately elevated," said Kenneth G. Woodring, Arch Coal’s executive vice president of mining operations. "Yesterday we succeeded in isolating the affected area from the rest of the mine. While we remain optimistic that the problem can be solved in a timely manner, it is possible that normal operations will continue to be suspended for a period of time. We do not believe the current situation will have a material long-term impact on the mine."

Higher-than-normal readings of carbon monoxide would suggest that combustion is present somewhere within the portion of the mine that has been isolated, Woodring noted. However, he reiterated that the levels are only moderately elevated and that gas levels seem to have stabilized. The above-normal readings were detected while the mine’s longwall mining equipment was routinely being moved to a new location inside the mine, but the two events are not believed to be related.

"Our first concern is for the safety of the West Elk employees," Woodring said. "We will not attempt to restart the mine until we are absolutely certain that conditions inside the mine are safe. We will continue to work around the clock in an effort to determine the cause of these readings and to pursue a safe resumption of mining operations." Woodring indicated that the company is working closely and cooperatively with the Mine Safety and Health Administration, which has officials on the site.

West Elk produced approximately 7.3 million tons of coal last year and employs around 300 people. Most of the mine’s output is sold to electric generating stations in the western and midwestern United States. Approximately 80% of West Elk’s output is produced with the longwall equipment, which employs a rotating drum that is pulled mechanically back and forth across a long face of coal. The loosened coal falls onto a conveyor system that carries the coal out of the mine. Two continuous miner units perform development work for the longwall and produce the remainder of the mine’s output.

Woodring added that it was too early to determine what impact West Elk’s temporary idling might have on Arch Coal’s financial performance.

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, including Arch Coal’s expectations with respect to the impact of certain operating events on future financial results. Although Arch Coal, Inc. believes the expectations reflected in such forward-looking statements are based on reasonable assumptions, it can give no assurance that its expectations will be attained. Factors that could cause actual results to differ materially from expectations include changes in local or national economic conditions; changes in mining rates and costs for a variety of operational, geologic, permitting, labor and weather-related reasons, including equipment availability; and other risks detailed from time to time in the company’s reports filed with the Securities and Exchange Commission, including quarterly reports on Form 10-Q, reports on Form 8-K, and annual reports on Form 10-K.

Arch Coal is the nation’s second largest coal producer, with subsidiary operations in West Virginia, Kentucky, Virginia, Wyoming, Colorado and Utah. Through these operations, Arch Coal provides the fuel for approximately 6% of the electricity generated in the United States.