Final answer:
High permeability in unconventional reservoirs would make hydraulic fracturing unnecessary, but this is atypical since these reservoirs generally require fracturing due to low permeability.
Step-by-step explanation:
The characteristic of source rocks in today's unconventional reservoirs that makes hydraulic fracturing unnecessary for recovering a sufficient amount of gas would be high permeability, which is not typically associated with unconventional reservoirs. Unconventional reservoirs usually feature rocks with extremely low permeability, such as shales, requiring advanced techniques like hydraulic fracturing to create permeability and extract hydrocarbons. However, if a reservoir does have naturally high permeability, the gas can flow freely without the need for fracturing, though this situation is rare for unconventional reservoirs.