Energy sources unsuitable for mobile power plants, such as nuclear power, renewable hydroelectricity, or wind power can be used. According to widely accepted global energy reserve statistics, the reserves of liquid fuel are much less than gas and coal (at 42, 167 and 416 years respectively). Most countries with large rail networks do not have significant oil reserves and those that did, like the United States and Britain, have exhausted much of their reserves and have suffered declining oil output for decades. Therefore, there is also a strong economic incentive to substitute other fuels for oil. Rail electrification is often considered an important route towards consumption pattern reform. However, there are no reliable, peer-reviewed studies available to assist in rational public debate on this critical issue, although there are untranslated Soviet studies from the 1980s.