Hello, I have the following question. I've read different articles and have noticed one thing. The phrase "demand for something" is used sometimes with the definite articles but sometimes without it. For example, there is an article about the oil market (the title is like this "oil prices fell by...."). The article is began with "demand for oil" without the definite article. But have read articles where the phrase is used with the definite article. I think when an article is about different commodities, then we use the definite article (for example, the demand for for oil and the demand for steel). Have I caught this right?