Alternatively, these reforming options can be combined to adjust the ratio between H2 and CO. Baltrusaitis et al. compare five combination configurations and deliver the conclusion that the combination of steam reforming and dry reforming is economically favored over other options. Also, such a combination can reduce carbon footprint by 67% over conventional steam reforming. Meanwhile, the existence of steam is preferred because the dry reforming suffers severe coke formation. Another novelty of combined reforming (CO2 + steam) is that CO2 is regarded as one of the raw materials. Thus, unlike the conventional process (autothermal reforming or steam reforming), a CO2 separation unit is not required before the reforming unit in the process design.