Which statement best describes the cost per foot relationship between air and mud rotary in unconsolidated formations?

• A. Air rotary generally lower cost per foot, but mud rotary may be more efficient at maintaining borehole stability.
• B. Mud rotary always yields faster drilling per foot.
• C. Air rotary usually costs more per foot and offers no stability benefits.
• D. Costs are unrelated to the rotary method.

Answer: (A)