Assertion: royalty trust | /r/CapableOf | involve oil and gas fields
Facets:
value: usually
type: TEMPORAL
Source sentences:
text: Additionally, royalty trusts in the United States and Canada usually involve oil and gas fields or mines which are at or past their production peak, and will gradually decline in output as well as revenue; however, the infrastructure to develop them has already been built, so that an investor can expect a reasonably steady income stream.