Shale resource systems include conventional source rocks, unconventional resources such as shale gas and shale oil system. Regardless of the type of shale resource system, the issues of petroleum formation processes (including petroleum generation, migration and storage) are very important in petroleum evaluation and exploration. Because of the complicated and different geological settings in the world, the evaluation approaches and workflows may not be easily implemented following those from successful examples. Thus, the mechanisms of petroleum formation are fundamental for petroleum exploration and production all over in the world. The reason this special issue focuses on the shale system is because the shale system is not only the main source rock type but also the main unconventional reservoir type in the world.