Confusing Terminology When Researching on Oil and Gas Industry

I am reading a book called The New Map: Energy, Climate, and the Clash of Nations. I learned that the United States become one of the top three oil and gas exporters in the world after discovering shale, and China imports around 70% of the local demand. This immediately sparks my interest to do a deeper search on the big picture of the energy market.

Then, I found a trade statistic database called BACI, which is an improved version based on Comtrade led by the United Nations which aggregates trade statistics by product and trading partner. Inside the database, products are classified using Harmonized System which is an internationally standardized system to classify traded products. When I try to search for petroleum, it returns multiple hits.

And the same for searching for Natural Gas. Even Coal, there are anthracite coal and bituminous coal (Explanation on the difference).

NGLs = Natural Gas Liquid
LPGs = Liquefied Petroleum Gas
LNG = Liquefied Natural Gas

Actually, they are all natural gas. How to distinguish them?

LNG is methane. NGL can be ethane, propane, normal butane or isobutane. NGLs are byproducts of natural gas processing and refining. NGL can be sold in pure form (90%) or mixed form. Propane, normal butane, and isobutane can also be labelled as LPG. The reason for having “petroleum” in its name is that these products can also be derived from the crude oil refining process.