Lignocellulosic agrowastes are one of the most abundant and inexpensive bioresources on earth. However, they comprise a wide range of materials with different organic and inorganic composition that may influence their performance in energy applications. Here, we analyze the impact of inherent inorganics on the steam gasification performance of bioresources, using an approach combining the analysis of the gasification reaction mechanisms, and the assessment of the process product distribution and energy balance. We proved that the inorganic ratio K/(Si + P) is a valuable indicator of the biomass gasification reactivity and product yield. Under the same experimental conditions, samples with K/(Si + P) higher than 1 followed a catalytic gasification behavior, resulting in higher gas yields and process gas efficiencies in comparison to samples with K/(Si + P) below 1. This work is expected to bring new insights in the field and could facilitate the adaptation of the process parameters to the feedstock characteristics and the application requirements.