As was first predicted by Ferrell and Prange, the Josephson tunnel current is limited to a strip of width approximately 2λJ, where λJ is the Josephson penetration distance, along the edges of the junction due to the magnetic field produced by the tunnel current itself. Using the symmetric geometry of Owen and Scalapino, we have investigated the maximum zero voltage d.c. current, I0, in a zero applied magnetic field of Sn–SnO–Sn junctions with widths W ~ λJ and various lengths L. The experimental data is compared with the theory of Owen and Scalapino by plotting (LI0)/(2λJWJ1) versus L/λJ, where J1 is the tunnel current density without self-limiting. The results are in reasonable agreement with the theory, except that I0 tends to be less than predicted. However, in most junctions the usual Fraunhofer pattern of maximum zero voltage d.c. current versus applied magnetic field is skewed, and better agreement with theory is obtained if the maximum zero voltage d.c. current in a magnetic field is used instead of I0.