[en] The design beam intensity of the FNAL Main Injector (MI) is 3 x 10¹³ ppp. This paper investigates possible limitations in the intensity upgrade. These include the space charge, transition crossing, microwave instability, coupled bunch instability, resistive wall, beam loading (static and transient), rf power, aperture (physical and dynamic), coalescing, particle losses and radiation shielding, etc. It seems that to increase the intensity by a factor of two from the design value is straightforward. Even a factor of five is possible provided that the following measures are to be taken: an rf power upgrade, a γ_t-jump system, longitudinal and transverse feedback systems, rf feedback and feedforward, stopband corrections and local shieldings