A feedstock flexible process for converting feedstock into oil and gas includes (i) indirectly heated hydrous devolatilization of volatile feedstock components, (ii) indirectly heated thermochemical conversion of fixed carbon feedstock components, (iii) heat integration and recovery, (iv) vapor and gas pressurization, and (v) vapor and gas clean-up and product recovery. A system and method for feedstock conversion includes a thermochemical reactor integrated with one or more hydrous devolatilization and solids circulation subsystems configured to accept a feedstock mixture, comprised of volatile feedstock components and fixed carbon feedstock components, and continuously produce a volatile reaction product stream therefrom, while simultaneously and continuously capturing, transferring, and converting the fixed carbon feedstock components to syngas.