LONDON (Reuters) -- Gas-rich Qatar is ploughing more of its commodity wealth back into the sector with the purchase of a major stake in Royal Dutch Shell while also reportedly eyeing a chunk of Italian oil major ENI.

A Shell spokeswoman confirmed the purchase while declining to detail its size but the Middle East Economic Survey reported earlier that Qatar's sovereign wealth fund was looking at a 3-5 percent stake.

If Qatar did buy 5 percent, it would be just ahead of Blackrock, which is currently Shell's biggest investor with 4.97 percent, according to Reuters data.

But British stock market rules require any party to disclose a holding of over 3 percent in a listed company so the absence of a statement from Qatar suggests its interest is below this level.

The Gulf nation's massive gas supplies have made it rich, allowing it to create a sovereign wealth fund that has been buying up assets, including stakes in listed companies, around the world.