The relationship between the leak rate of hydrocarbons (HC) and helium through small channels is being evaluated. Measurements of the flow of HC down micro-channels through walls are compared with theoretical models. It is shown that a realistic model for fuel micro-leaks is that of a channel with length/diameter >> 1. HC flow through such channels is shown to be laminar for driving pressures of at least 3 kPa. These results may be used to provide upper bounds for fuel loss estimates using helium leak detection techniques.