By Anna Hirtenstein

Jan 22 (Reuters) - Saudi Arabia's state oil company Aramco bought its first cargo of WTI Midland, a U.S. crude oil grade that underpins the global Brent benchmark, oil-index publisher S&P Global Commodity Insights said on Wednesday.

Aramco, the world's largest oil firm, snapped up the cargo on Tuesday in the so-called Platts trading window, buying from trading firm Gunvor. Platts is a division of S&P Global.

This was Aramco's first WTI purchase in the window, said Joel Hanley, global director of crude and fuel oil markets at S&P, via email on Wednesday. Aramco declined to comment.

More players have become involved in trading crude that can set the Brent price via Platts since it added WTI to the benchmark in 2023. Aramco, which has been expanding its trading activity, first traded WTI last February, as a seller.

"National oil companies are building up trading activity to gather information and top up income," said Adi Imsirovic, director at consultant Surrey Clean Energy and a veteran oil trader who has written extensively on Brent.

"Aramco has clearly made a decision to get more involved in trading - we will see more and more of this."

In an interview at the World Economic Forum in Davos, Switzerland on Tuesday, Saudi Arabia's energy minister said that he views the oil market as healthy and expects another 1.3 million barrels per day of demand this year.

WTI Midland is one of six crude oil grades assessed by Platts that can set the value of dated Brent, part of the wider Brent complex used to price more than three-quarters of the world's traded oil.

The dated Brent price is set by the cheapest of the six crudes and Midland, the largest of the six streams, often plays a role in setting its value. The other five are North Sea crudes.

(Reporting by Anna Hirtenstein, additional reporting by Yousef Saba, editing by Alex Lawler and Kirsten Donovan)

((Anna.Hirtenstein@thomsonreuters.com;))