(Bloomberg) —

Recently, there has been a sharp increase in freight rates for tankers transporting oil, prompting many vessels to shift their operations toward this profitable trade. Numerous ships have changed from carrying refined products to transporting crude oil across global waters.

In just the first four days of this month, nine long-range 2 (LR2) tankers—large vessels that usually transport products like jet fuel and diesel—began carrying crude oil instead, based on data from the ship-tracking platform Signal Ocean. This brings the total number of switches from transporting clean products to dirty oil to 35 this year.

This shift in some parts of the tanker fleet highlights the influence of oil-producing countries increasing their output, along with the repercussions of stricter Western sanctions on Russia and Iran. OPEC+ and non-member drillers have both increased supply this year, resulting in more crude oil that needs to be shipped to buyers.

“Shifting to dirty cargoes was expected,” said Georgios Sakellariou, a chartering analyst at Signal Maritime, a company that manages tanker pools and is associated with Signal Ocean. “What used to be a minor operational choice for shipowners has now become a significant market trend.”

Sakellariou noted that the potential for higher earnings from transporting oil is motivating this transition.

The earnings for very-large crude carriers have recently reached their highest levels in years. This surge in rates is also benefiting smaller tankers, such as Aframaxes, which are the crude oil equivalents of LR2s, allowing them to charge significantly higher rates. An LR2 that switches to carrying crude can set prices similar to Aframax rates.

In early September, LR2 tankers briefly had slightly better earnings than Aframaxes. However, just two months later, Aframaxes are now earning $65,500 per day as of Tuesday, according to Jefferies LLC. This represents almost a 70% premium over the daily rates for LR2 tankers.

While switching tankers between transporting clean and dirty cargoes is common in the industry, this transition comes with costs.

To shift from dirty to clean, tank owners must pay for new coatings to prepare for transporting refined products. Conversely, those moving from clean to dirty must consider the costs associated with existing coatings being damaged.