Cryptocurrency entrepreneurs are fueling their operations with a source of natural gas that frequently gets wasted during oil production, but experts worry there could still be an environmental cost. Across the United States, companies are setting up shipping containers where racks containing hundreds of computers mint cryptocurrency, fueled by natural gas from oil wells that otherwise would be burned off as waste. "If we weren't here, at this site, they would be flaring off this natural gas and burning it in a little torch on the well site," says Matt Lohstroh, the co-founder of the natural gas bitcoin mining company Giga Energy in Houston, Texas. IMAGES AND SOUNDBITES