Why is Trinidad’s natural asphalt the only commercially viable one?

Asphalt-like deposits found elsewhere in the world are either below water, of a quality not suitable for use in the road industry or are below the earth such that it can be mined, but at some expense, such as those found in the USA, called gilsonite. Surface mining available to TLA does not only make TLA more cost effective, but its high quality, as sanctioned by global asphalt authorities, also bring merit to its claim of “….only commercially viable.”