These essential elements and processes must be correctly placed in time and space so that organic matter included in a source rock can be converted into a petroleum accumulation. A petroleum system exists wherever all these essential elements and processes are known to occur or are thought to have a reasonable chance or probability to occur. | These essential elements and processes must be correctly placed in time and space so that organic matter included in a source rock can be converted into a petroleum accumulation. A petroleum system exists wherever all these essential elements and processes are known to occur or are thought to have a reasonable chance or probability to occur. |