By Ryan Dezember and Mike DeStefano

The most wagered-upon oil prices these days are for crude bobbing at sea on big tankers -- or even still in the ground.

In futures markets for both overseas-benchmark Brent and West Texas Intermediate, the main U.S. price, barrels for December delivery have the highest open interest, or total number of options and outstanding contracts.

It is unusual for betting to center on barrels scheduled for delivery so far into the future. The most open interest almost always relates to oil for delivery the next month, or sometimes the month after that.

The situation reflects traders' aversion to near-term contracts as long as the coronavirus pandemic is pummeling fuel demand. Front-month West Texas Intermediate futures last month crashed below $0 as buyers already swamped with oil fled the market. The popularity of the December contracts also indicates optimism that prices will rebound later this year as shelter-in-place orders are eased.

In data going back to 2006, there hasn't been another instance in which a West Texas Intermediate contract seven months out had the greatest number of bets related to it, according to Dow Jones Market Data. On only one other occasion -- exactly four years ago -- has the greatest open interest been in the sixth Brent contract out, which in that case was December's.

West Texas Intermediate futures for June delivery gained 8.1% on Monday to end at $31.82 a barrel. It was the highest closing price since March 11, before much of the U.S. was under stay-at-home orders to stem the spread of the deadly coronavirus.

Contracts for barrels to be delivered in December closed at $34.07. A barrel of Brent for December settled at $37.11, 6.6% higher than July's price of $34.81.

The differences were much larger last month, when fuel consumption nosedived and unprocessed crude and unsold petroleum products overwhelmed storage facilities and refineries. Prices for on-the-spot deliveries of oil plunged, as did those for prompt futures contracts.

As near-term crude prices collapsed, the massive exchange-traded U.S. Oil Fund spread out its exposure deeper into the calendar. Since its launch in 2006, the fund had held all of its assets in one of the two front months of West Texas Intermediate futures. By Friday, the $4.1 billion fund, which is popular with day traders and hedge funds alike, held $1.02 billion of December futures. Its next-largest exposure was to August futures, to the tune of $623 million.

Energy traders have done particularly well this year betting on near-term oil prices to fall while wagering on rising prices later in the year. So-called carry trades involving West Texas Intermediate this year have earned better than 80% on annualized basis, according to Bank of America Securities analysts.

In a note to clients, they said carry trades have historically performed well even after supply gluts peak and suggested such trades as a hedge against a second viral outbreak.

The opportunity to profit by holding oil back from the market until prices rise -- or at least not losing money selling crude for less than it cost to extract -- stoked a run on oil-storage capacity as well as oceangoing tankers.

"Our storage is worth its weight in gold," said Jim Teague, chief executive of Enterprise Product Partners LP, which owns pipelines, storage facilities and export terminals. "Our people have found places to store crude oil that two months ago we didn't even know existed."

Hess Corp. said that rather than shut in its North Dakota wells, it is storing crude at sea.

Hess chartered three very large crude carriers, or VLCCs, and will fill one of the 2-million-barrel tankers during each of May, June and July with plans to sell the cargoes in Asia late this year.

The tankers' cost, which has shot up during the pandemic, is more than covered by the higher prices that Hess was able to lock in hedging in the futures market and by moving the oil from the domestic market and into the higher-priced Brent market.

"You're actually getting a value uptick because of moving it out of the United States, where oil is locked up, into a market that will take it," CEO John Hess told investors recently.

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Write to Ryan Dezember at ryan.dezember@wsj.com

Corrections & Amplifications

This article was corrected on May 19, 2020 because the original version incorrectly said the June 2020 contract for West Texas Intermediate futures expires on May 18. Its final day of trading is May 19.