Addressing the urgent need for renewable, carbon-neutral, and locally sourced alternatives to fossil fuels amid ongoing climate change and geopolitical tensions, the quest for green fuels intensifies. Photocatalytic conversion of fatty acids to hydrocarbons by Fatty Acid Photodecarboxylase (FAP)1,2 emerges as a promising pathway. Despite prior concerns about its efficacy on C2-C12 fatty acids, recent findings challenge this assumption. Our results3 unveil that Chlorella variabilis FAP (CvFAP) demonstrates significantly enhanced activity, converting octanoic acid four times faster than hexadecanoic acid, its best substrate reported to date. Moreover, in vivo experiments reveal a remarkable ten-fold increase in CvFAP-based production rates for n-heptane compared to n-pentadecane. Time-resolved spectroscopy and molecular modeling shed light on the underlying mechanism, revealing an autocatalytic effect of n-heptane contributing to the high catalytic activity of FAP on octanoic acid3. These insights pave the way for future FAP enhancement strategies, marking a crucial milestone towards the bio-based, light-driven production of gasoline-like hydrocarbons.