What process causes organic remains to turn into fossil fuels?

The process that transforms organic remains into fossil fuels is called diagenesis and subsequently catagenesis. Initially, organic matter, such as plant and animal remains, accumulates in sedimentary environments, where it undergoes decay and compaction. Over millions of years, heat and pressure from overlying sediments convert this organic material into hydrocarbons through chemical reactions. This process ultimately leads to the formation of fossil fuels like coal, oil, and natural gas.