The first crude stream to turn upside down was Wyoming Asphalt Sour, a dense oil used mostly to produce paving bitumen. Mercuria Energy Group Ltd., a trading house, bid negative 19 cents per barrel in mid-March for the crude, effectively asking producers to pay for the luxury of getting rid of their output.

“These are landlocked crude with just no buyers,” said Elisabeth Murphy, an analyst at consultant ESAI Energy. “In areas where storage is filling up quickly, prices could go negative. Shut-ins are likely to happen by then.”

Brent and West Texas Intermediate, the benchmarks closely followed in Wall Street, are hovering above $20 a barrel. But in the world of physical oil — where actual barrels change hands — producers are getting much less as demand plunges due to the lockdown to contain the spread of the coronavirus.

Oil traders believe other crude streams are likely to see negative prices soon at the well-head as refiners reduce the amount of crude they process, leaving some landlocked crude without easy access to pipeline trapped.

Several crude grades in North American are already trading inside the single digit territory as the market tries to force some output to shut-in. Canadian Western Select, the benchmark price for the giant oil-sands industry in Canada, fell to $5.06 a barrel on Friday. Southern Green Canyon in the Gulf of Mexico is worth $11.51 a barrel, Oklahoma Sour is changing hands at $5.75, Nebraska Intermediate at $8, while Wyoming Sweet prices at $3 a barrel.