石油由原油和天然气组成，它们似乎来源于海洋沉积物中的有机物质。
Petroleum, consisting of crude oil and natural gas, seems to originate from organic matter in marine sediment.
原油和天然气的生产占了GDP的近半数。
Crude oil and natural gas production account for nearly half of GDP.
与历史标准相比，原油和天然气的价格仍然相对较高，但是自7月以来已经下跌了一半。
Oil and gas are still relatively expensive by historical standards, but the prices have fallen by half since July.
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