Assertion: natural gas | /r/MadeOf | propane
Facets:
value: usually
type: TEMPORAL
Source sentences:
text: Such natural gas is known as associated gas; it is often considered to be the gaseous phase of the crude oil and usually contains some light liquids such as propane and butane .
text: Natural gas is extracted from deep within the earth and can contain ethane, propane, butane and pentane.