The chemical industry accounts for 20% of global industrial greenhouse gas (GHG) emissions and the plastics production is increasing worldwide by approx. 4% annually. To reduce GHG emissions and increase GHG transparency in chemical value chains despite industrial secrets, we developed an approach to estimate the product carbon footprint of chemicals site-specifically without using classified production data. The new approach, is applied to two comparative case studies: propylene and toluene diisocyanate (TDI) production in Germany. The case study analyses 23 crackers on 17 production sites and four TDI production sites in Germany. The results indicate significant GHG emissions variations between productions sites (Cradle-to-Gate) that could not be quantified before. Among the production sites, product-specific GHG emissions range between 0.95 and 1.51 kgCO2e/kg propylene (reduction potential of GHG emissions of 37.1%) and between 3.17 and 3.62 kgCO2e/kg TDI (reduction potential of GHG emissions of 12.4%). This indicates massive differences in GHG efficiency in the production of propylene and TDI and an immense GHG emission reduction potential in the manufacture of plastic-intensive products (e.g. ... mehrin the automotive sector) by increased transparency and informed supplier selection and procurement decision making. The method is transferable to chemical sites worldwide and indicates an even higher GHG reduction potential worldwide.