OPEC and non-cartel members may be employing a wrongheaded approach to shrinking a global supply glut, according to Dieter Helm, economist and Professor of Energy Policy at the University of Oxford in the U.K.

Speaking at the International Petroleum Week in London last week, Helm struck a decidedly dour outlook on the oil industry, arguing that history suggests prices are only heading one way—down. That means, if you are a member of the Organization of the Petroleum Exporting Counties or another major oil producer, you should boost production, rather than scale it back.

“For the NOC’s (National Oil Companies) in the Middle East and elsewhere, increasing production is quite a good idea, because you’re going to need the money and you might as well get your stuff out of the ground now rather than later. So, the opposite of what’s currently happening,” Helm said.

Read:Why oil prices will never return to $100 a barrel, in one chart

After months of speculation, negotiations and anticipation, OPEC and 11 non-OPEC producers, including Russia, came together in December and hammered out a historic deal to curtail oil production. The idea was to make a dent in the world’s oversupply, which has hammered prices that peaked at more than $100 a barrel back in 2014.

The deal has largely been credited with lifting oil prices US:CLJ7 UK:LCOJ7 about 20% in recent months and has been hailed as a success by the participating nations.

Read:OPEC output deal made ‘remarkable impact’ on oil prices, Qatar minister says

But Helm says—regardless of any OPEC action—prices are going to fall, which means oil today is worth more than oil tomorrow. From that perspective, there is no incentive to leave oil in the ground longer then necessary as you would make less profit on it in the future than you would right now.

Read:The 3 major risks keeping oil executives up at night

Even $50 oil is high in historic view

Of course, the big question is whether oil prices will in fact head lower in coming years. Delegates at the London conference were optimistic that prices could remain around $55 or higher, but historic data offer a different outlook, according to Helm.

“$50 oil is a very high price for oil and over the next decade or so the price of oil will probably carry on gradually falling, as it did for 100 years, between 1870-1970,” he said.

Helm says there isn’t a direct correlation between demand for oil and a rise in prices (i.e., higher demand doesn’t necessarily result in higher fuel prices), based on historical data. “It didn’t [between 1870 and 1970]. And it probably won’t in the future,” he said.

BP

As the chart from BP BP, -3.47% UK:BP shows, oil prices—adjusted for inflation—gradually moved lower for a century, before political unrest in the Middle East in the 1970s coincided with a sharp rally. Then prices reverted closer to their historic average until oil prices jumped above $100 amid the Arab Spring in 2011.

Higher oil prices may have encouraged a ramp up in production, particularly in the U.S., which created such a supply glut that prices came crashing down in 2014.

Crude oil bottomed out below $27 a barrel in Feb. 11, 2016 and has since soared to trade around $54, partly due to OPEC’s efforts.

“So, OPEC may have cobbled together something for six months, in my view relatively ineffectively, but this is a temporary dam and it is very, very likely that it will fail,” Helm said.

The Oxford professor and author of several oil-related books also offered other arguments as to why its game-over for rising oil prices. The sharper focus on climate change will decrease demand for fossil fuels, he said, while digitization means less need for transporting people and goods around.

To be sure, not everyone is downbeat on the future for oil. Citigroup strategist earlier this week said Brent oil could rally to $70 by year-end, while Phil Flynn, senior market analyst at the PRICE Futures Group, said they have been targeting $73-a-barrel for U.S. crude and $71-a-barrel for Brent since January.

At the International Petroleum week conference in London, which featured some of the oil industry’s key figures, the sentiment among oil executives was relatively upbeat.