The abundance of liquefied natural gas (LNG) supplies made possible by unconventional technology is so great that the U.S. is destined to become a prolific exporter of the fuel. Sound familiar?

While this theory has become a mantra for many in the oil and gas business, Kenneth Medlock, a fellow at Rice University’s Baker Institute in Houston, is not joining the sure-thing theorists. Amid all of the exaltations for exportation, Medlock contends that some complications exist.

In other words, borrowing a line from a Louis Armstrong standard, the bucket’s got ...