Crude oil prices continued their decline on Thursday, with the American benchmark dropping below $90 a barrel during the day and its main international equivalent falling as well.

Now at their lowest levels since 2012, crude prices have been under pressure in recent months. The increase in global demand for oil this year is turning out to be slower because of weaker-than-anticipated growth in China and Europe, while oil supplies remain strong, leading to growing inventories.

But the sudden drop on Thursday was seen as a response to Saudi Arabia’s signaling on Wednesday to the markets that it was more interested in maintaining market share than in defending prices. Saudi Aramco, the national oil company, stunned markets by announcing that it was cutting prices by about $1 a barrel to Asia, the crucial growth market for the Persian Gulf producers, as well as by 40 cents a barrel to the United States.

With oil prices already under pressure, “there has been a widespread perception or hope that the Saudis would pull back on production,” said Richard Mallinson, an analyst at Energy Aspects, a research firm based in London.