<P> Natural gas originates by the same geological thermal cracking process that converts kerogen to petroleum . As a consequence, oil and natural gas are often found together . In common usage, deposits rich in oil are known as oil fields, and deposits rich in natural gas are called natural gas fields . </P> <P> In general, organic sediments buried in depths of 1,000 m to 6,000 m (at temperatures of 60 ° C to 150 ° C) generate oil, while sediments buried deeper and at higher temperatures generate natural gas . The deeper the source, the "drier" the gas (that is, the smaller the proportion of condensates in the gas). Because both oil and natural gas are lighter than water, they tend to rise from their sources until they either seep to the surface or are trapped by a non-permeable stratigraphic trap . They can be extracted from the trap by drilling . </P>

Why are gas deposits found on top of oil deposits
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