The best argument for an optimistic view of oil prices that plunged to negative territory this week is that it is a local problem.

The negative price of oil means, the strange negative pricing is no longer so mysterious. It is customary to talk about the price of the West Texas Intermediate (WTI) variety at the Cushing, Oklahoma terminal as if it is representative of the oil market as a whole, but this has never been the case. The double shock (in supply and demand) of the global oil market has made the shortage of storage capacity at this particular site so acute that producers are willing to pay to dispose of their goods. This should not matter more broadly.

Although the WTI has always been a less important measure in the oil market than it seems, the current turmoil creates deeper problems. The Brent variety, which is the benchmark for more than two-thirds of the world’s oil, may face similar difficulties if current low prices continue.

Although the Brent futures are settled in cash, which means that there is no need to accept the physical delivery that causes such problems in Cushing, they are closely linked through derivatives to the Dated Brent index, which is an amalgam of physical prices at five terminals at the North Sea coast.

Taking the North Sea as a price point has advantages over Oklahoma: Terminals in this sea are open to world tanker trade, and production has declined in recent years. As a result, the Cushing situation is less likely to recur.

However, there is no guarantee of this. Total storage capacity at the five Dated Brent terminals is approximately 31 million barrels, which is approximately one-third of the 93 million barrels available in Cushing. Their ability to land tanker loads is affected by the same manufacturing glut that damages WTI. In fact, one of the best options for shale producers in North America looking to avoid a collapse in Oklahoma is to redirect their barrels of sweet, light Brent crude oil to Houston for delivery to Europe.

The most important of the varieties that make up the Brent basket is currently Forties, which is shipped from a terminal east of Edinburgh. The Ineos Group, which manages the terminal and the associated pipeline network, announced last month that it would delay scheduled shutdowns for customer service requests. That should push shipments from the North Sea to more than 3 million barrels per day in July, the highest level since 2011, according to consulting firm Rystad Energy.

Meanwhile, as tankers are converted to temporary storage facilities, the cost of transporting crude oil from Europe to Asia has increased from levels below 2 USD per barrel to over 6 USD per barrel in the last month – a significant increase when Brent itself is below 20 USD per barrel. If these transportation costs rise further, they will begin to put as big a financial barrier on exports from the abundant Brent terminals as there are physical restrictions in Cushing.

Those who trade in real supplies rather than paper seem to notice. Dated Brent fell to 13.24 USD on Tuesday, according to S&P Global Platts, and the discount on futures is at record highs. Negative prices still seem unlikely, but they also seemed unlikely for WTI until Monday.

More importantly, Dated Brent does not need to go into negative territory to push a huge share of the world’s oil production in red. Middle Eastern and African varieties are quoted at some discount to Dated Brent or several other contracts, which themselves usually follow physical shipping from the North Sea. For some heavier varieties, such as Saudi Arab Heavy or Iraqi Basrah Heavy, these reductions can often exceed 10 USD per barrel, worryingly close to the levels at which Dated Brent is traded recently. The Mexican Maya has already fallen below zero once this week, thanks to exactly the kind of pricing formula that links it to WTI.

There are methods for dealing with problems with Dated Brent terminals. The physical and intangible markets for the North Sea oil industry are linked by a complex derivative system that allows pricing companies to change their methodologies if physical trading is too “short”, with billions impact, putting enormous pressure on a system that has never been designed for such situations.

For a generation, the global oil market depended on monitoring the prices of crude oil passing through several places, with physical players watching the futures market for reassurance. If this system breaks down, the star will be lost and confusion reigns. Do you think the volatility of the oil market has disappeared after this week? Don’t count on it.