Many economists warn that global oil reserves are being depleted at an alarming rate.

oil的意思是"石油"，指从地下开采出的液态矿物燃料。 reserves是名词reserve的复数形式，reserve本义是"储备、储存"，指保存起来以备将来使用的资源。 oil reserves指一个国家或地区已探明但尚未开采的石油储量，是衡量能源安全的重要指标。