Here's the biggest problem facing the oil market: Its No. 1 customer has disappeared.

The shutdown of parts of the US economy -- roughly half of Americans are under at stay-at-home orders -- has crushed demand for gasoline. And US gasoline is the No. 1 swing far worldwide thirst for oil.

IHS Markit estimates that US gasoline demand could collapse by as much as 4.1 million barrels per day -- or more than 50% -- during the coronavirus response period . That easily exceeds the demand destruction during the Great Recession.

"A sudden drop in miles traveled by car triggered by social isolation measures will have immediate ramifications for gasoline demand," IHS wrote in a report published Thursday.

The pandemic has caused congestion in the 10 most heavily trafficked US cities to nosedive by 76%, according to RBC Capital.

That's because millions of Americans are now working from home. The amount of gasoline consumed by Americans commuting to and from work exceeds all of China's gasoline demand, RBC said.

At the same time, Saudi Arabia and Russia have flooded the market with excess supply. No wonder oil dropped to 18-year lows.