The premium for prompt U.S. crude futures to the second-month contract more than doubled on Tuesday, hitting a high of $1.90 a barrel - its widest level in roughly four months.
The structure, known as backwardation, occurs when the front-month contract is at a premium to later-dated contracts and can indicate tightness in the market. It gives energy companies little incentive to pay to store their product for future months, but rather to sell while prices are firmer.
At the end of last week, the front-month contract was at roughly at 78 cent a barrel premium to the second month.
Prompt futures traded at a discount to future month contracts as recently as Feb. 8.
The WTI March contract expires on Tuesday and volumes were thin.
The difference between the more liquid April contract and May was 45 cents, its steepest since early November.
