Oil prices slipped on Tuesday as vaccine optimism was overshadowed by concerns over fuel demand in the near term in coronavirus-hit United States and Europe returned to haunt the market.

U.S. West Texas Intermediate (WTI) crude futures was down 60 cents, or 1.5%, to $39.69 a barrel at 07:09 am, while Brent crude futures was down by 54 cents, or 1.3%, to $41.86 a barrel.

Both benchmark contracts climbed 8% on Monday in their biggest daily gains in more than five months after drugmakers BioNTech and  Pfizer said an experimental COVID-19 treatment was more than 90% effective based on initial trial results.

On Tuesday, U.S. oil inventory numbers are due from the American Petroleum Institute, and from the Energy Information Administration on Wednesday.