A drilling technique known as "hydraulic fracturing", where a mix of water and chemicals are blasted under-ground to create fissures in gas-bearing rocks, has made it much easier and cheaper to extract gas from shale, coal, and other less permeable geological formations.
A. known as "hydraulic fracturing", where a mix of water and chemicals are
B. known as "hydraulic fracturing", in which a mix of water and chemicals is
C. is known as "hydraulic fracturing", in which a mix of water and chemicals are
D. is known as "hydraulic fracturing", in which a mix of water and chemicals is
E. known as "hydraulic fracturing", which is a mix of water and chemicals
A. known as "hydraulic fracturing", where a mix of water and chemicals are
B. known as "hydraulic fracturing", in which a mix of water and chemicals is
C. is known as "hydraulic fracturing", in which a mix of water and chemicals are
D. is known as "hydraulic fracturing", in which a mix of water and chemicals is
E. known as "hydraulic fracturing", which is a mix of water and chemicals













